At 7pm on February 2nd, the 2026 January transfer window officially closed, bringing an end to clubs’ transfer business, but the biggest story might not have been a signing – it was a failed medical.
During this period, players completed moves after both clubs reached a financial agreement, exchanged all required documents and the individuals underwent the necessary medical procedures.
While the majority of transfers were successfully finalised, it was Crystal Palace striker Jean-Philippe Mateta’s failed medical that ultimately grabbed the attention of football fans around the world.
With AC Milan eager to bolster their attacking options, the Rossoneri shifted their focus to the Eagles’ target man, who has netted 46 Premier League goals across six seasons and played a key role in delivering Palace’s first-ever FA Cup triumph.
However, despite negotiations nearing a conclusion, the move ultimately collapsed after the French striker reportedly failed his medical, with Milan determining that he would likely need knee surgery to address suspected inflammation.
The news of Mateta’s failed medical comes as something of a surprise, especially considering that out of hundreds of completed transfers, AC Milan chose to withdraw from this particular deal.
It is not as though clubs have never signed players with previous injury concerns, but Milan may have been keen to avoid any potential financial risks, particularly as Mateta was expected to commit to a long-term contract.
In this article, we explore five key reasons why a failed medical can occur in football transfers — ranging from recurring injury issues to concerning scan results and failed physical tests.
The Top Five Reasons For A Failed Medical
Historical Tissue Damage
This can be the most common reason footballers fail medicals.
Clubs can decide against continuing the deal not because the players were “unfit” and not athletic enough but because of insurance risks and potential long-term health concerns.
A player who easily comes to mind as one who has struggled with persistent tissue damage caused by a knee injury is Victor Boniface.
The talented Nigerian international, who made history by becoming the first player in the Bundesliga to win the Rookie Of The Month five consecutive times, saw his chance to move to AC Milan fall apart due to scar tissue concerns.
Boniface, who has suffered two separate Anterior Cruciate Ligament ruptures in his right knee (in 2019 and 2020) was unable to complete the move as the club doctors identified abnormalities and structural instability during a rigorous 48-hour medical examination in August 2025.
Despite his failed medical, Boniface was able to secure a move to Werder Bremen on a season-long loan on the final day of the 2025 summer transfer window.
At the time of writing, Boniface is sidelined for the remainder of the season after undergoing successful surgery to address the persistent knee issues.
There have also been several high-profile players that have seen their dream moves collapse due to tissue damage.
Players like Hakim Ziyech (Chelsea to Al Nassr), Nabil Fekir (Lyon to Liverpool), and Demba Ba (Hoffenheim to Stoke) are all examples of failed medicals due to effects of past injuries.
Cardiac Anomalies And Heart Health
Similar to how Newcastle United took a major gamble on Demba Ba despite being aware of his problematic knee, most clubs would be far more cautious when dealing with a player with a heart irregularity.
This type of situation is often regarded as the “Red Zone”, as the potential risk goes beyond football and could be a matter of life and death.
A transfer to a new club cannot be finalised without the club’s medical team carrying out an Electrocardiogram (ECG) and echocardiogram. These tests are conducted to identify any abnormal heart rhythms.
While there have been numerous instances of transfers collapsing because of abnormalities discovered in medical tests, one remarkable and inspiring case stands out — that of Nigerian and Arsenal legend Nwankwo Kanu.
When he was set to move from Ajax to Inter Milan in 1996, his medical examination uncovered a serious heart valve defect.
Kanu subsequently underwent life-saving surgery, made a successful return to football, and went on to enjoy an illustrious career at Arsenal, where he won two Premier League titles, two FA Cups, and a Community Shield.
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Isokinetic Imbalance (Muscle Weakness)
Imagine a striker valued at €35 million who appears to train well and shows no sign of discomfort on the pitch, but tests reveal his hamstrings are 20% weaker than his quadriceps.
This imbalance is uncovered during isokinetic testing — often referred to as the “silent predictor” of future hamstring injuries — a medical assessment that uses specialized machines to detect issues that are not visible to the naked eye.
Before a player signs, the X-Rays and MRIs look at bones and ligaments, but the isokinetic test measures raw power and symmetry.
In modern football, clubs now use a specialised machine, often a Biodex chair, to measure the power of a player’s quads and hamstrings.
The aim of this test is to ensure that one leg is not significantly stronger than the other and that the ratio between the front and back muscles is balanced. If the test eventually reveals a deficit of 15-20% in one limb, it is a massive red flag that could lead to a failed medical.
The Surprising Dental Connection
Imagine the shock on a player’s face when they hear that the main reason for their transfer collapse is because of their teeth.
As surprising as it may seem, this is the reality for a small number of players whose moves have fallen through right at the final hurdle. This is not about having the perfect smile, it is about chronic inflammation.
One of the most “secret” factors behind a failed medical is poor oral health. To the ordinary football fan, a cavity or a toothache should be irrelevant to a player changing clubs, but for a sports scientist, it is a major red flag and another way a failed medical happens.
The science is simple: infections in the teeth or gums can cause systemic inflammation and this inflammation travels through the bloodstream and weakens the body’s soft tissues.
A player who might be struggling with recurring hamstring injuries might actually be suffering from a hidden dental infection.
The most well-known case of a “dental issue” involves French defender Aly Cissokho, whose €15 million transfer from Porto to AC Milan collapsed after club doctors deemed his teeth to be “misaligned”.
The player later went on to play for nine different clubs after the failed move.
Financial And Insurance Risk Assessment
In the modern era, a footballer is not just an athlete, he is an investment, a multi-million-pound asset that must be insured and failure to do so could lead to a financial catastrophe for the club.
While the doctor’s office is where a medical begins, the boardroom is often where it ends. The final – and perhaps most cold-blood – reason for a failed medical is the inability to secure comprehensive insurance coverage.
If an insurance company knows about a “pre-existing condition” in a player’s knee or heart and refuses to cover it, the club is left unprotected.
Rather than risking a total loss on an uninsurable player, boards will often pull the plug on the deal, proving that a failed medical is sometimes more about a calculator than a stethoscope.
Main Photo
Credit: IMAGO/Sportimage
Recording Date: 25.01.2026
