A compensation case brought by West Bromwich Albion football club against a surgeon could result in many similar cases, the appeal court has been told.
Michael Appleton had to retire at the age of 27
The club is claiming £1m in compensation against knee specialist Medhet Mohammed El-Safty.
They claim his advice to operate on a knee injury to midfielder Michael Appleton was unnecessary.
Lawyers for the surgeon told judges the case could result in an avalanche of cases brought by clubs against doctors.
West Brom began the claim over treatment to the midfielder who suffered a cruciate knee ligament injury in a training-ground accident in 2001.
The £750,000 signing was referred to the specialist who advised reconstruction surgery.
But the former Manchester United trainee never recovered and was forced to quit the game two years later aged 27.
West Brom claim the operation should never have gone ahead and if that had been the case the player would still be on the pitch.
The case centres on whether there was a contractual obligation between the specialist and the club.
Stephen Miller, acting for the specialist, said that, if West Brom won the case, the floodgates would be opened for a large number of potentially very high value claims against doctors not by their patients, but by their patients' employers.
A judge at the High Court last year rejected the claim ruling the surgeon had no contractual duty to the club.
At the Appeal Court on Thursday Mr Miller said: "It has been admitted that it was negligent to have advised surgery at the outset and that conservative measures should have been tried first.
"Had they been, they would probably have been successful."
But he added the claim still failed without proof that Mr El-Safty owed the club a "duty of care" recognised by the law of negligence.
The appeal judges in the case are expected to reserve their decision on the club's appeal until a later date.