Owen Hargreaves says he felt as though he was "made of glass" and had to be a "guinea pig" during treatment for knee injuries when he was at Manchester United.
Hargreaves, whose three-year fitness nightmare at Old Trafford meant he played just six minutes of first-team football since September 2008 following double knee surgery to resolve a tendinitis problem, emerged from the wilderness with a goalscoring debut for Manchester City in Wednesday's League Cup victory against Birmingham.
The 30-year-old midfielder, now attempting to relaunch his career at the Etihad Stadium after being released by United at the end of last season, claims he was left to "pick up the pieces" following the unsuccessful attempts to overcome his injuries at Old Trafford.
When asked whether he believed his injuries had been mishandled by United, Hargreaves said: "You'd have to ask them (United), but there were a few crucial points at times."
United declined to comment on Hargreaves's allegations yesterday. However, they have an unquestioned reputation for medical care of players and there is no evidence of misdiagnosis or mistreatment in this case.
"I received some injections but my tendon was never the same," the former England midfielder continued.
"After the injections, I tried to get back on my feet and they said my tendon was good, but it felt like I was made out of glass. That obviously had a huge impact.
"With my tendon injury, I've had to be a guinea pig for a lot of these treatments. It's difficult. All the people there (at United) are lovely and everybody tries their best, but at times you come to a certain point where you need to make a decision.
"They said it would help. Basically, I was left to pick up the pieces, which was incredibly frustrating."
Hargreaves spent time with the American surgeon Richard Steadman, Vancouver-based physiotherapist Alex McKechnie and German doctor Hans Muller-Wohlfahrt during his battle to return to fitness.
"I wanted to play," Hargreaves said. "Everyone wanted me to play, so it's not really an option to say, 'sit it out and rest for six months'.
"With hindsight it's a lot easier, but I wish I had not had the injections."