Manchester United have defended their medical treatment of Owen Hargreaves after he said he felt like a "guinea pig" while recovering from injury.
The midfielder, who barely played in his last three seasons at Old Trafford, has alleged his comeback was affected by a course of pain-killing injections.
"I've had to be a guinea pig for a lot of treatments," said Hargreaves, who joined Manchester City in the summer.
A United statement said: "The club gave him the best possible care."
It added: "The club is as disappointed as anyone he was not able to play a part in the team's success [over the last three years].
"It has shared all the medical records with Manchester City and is comfortable with the actions taken by its medical staff at each step of his many attempts at rehabilitation.
"Manchester United has some of the best sports medical staff in world sport."
Reds boss Sir Alex Ferguson last year admitted to having concerns over Hargreaves' ability to make a successful comeback from his injury problems.
But he said on Friday: "Our doctor and his five physios are fantastic.
"As far as I am concerned my medical staff are one of the main reasons why we have been so successful over the last few years.
"Do you think we would be successful if they were not 100% brilliant? That is my opinion and that is more important than what anyone else has to say about it."
Hargreaves, 30, spent four seasons at Old Trafford but persistent tendinitis meant the player had to have double knee surgery during the 2008-09 season.
However, he revealed the problems began in his first season at United, following his £17m move from German side Bayern Munich.
"I received some injections and my tendon was never the same," he said in an interview with several national newspapers.
"I tried to get back on my feet and [United's medical staff] said my tendon was good, but it felt like I was made of glass.
"[The injections] obviously had a huge impact. With hindsight, I probably should not have had them. It's difficult."
Hargreaves also suggested that he was pressured to play in a Premier League game against Wolves last season.
It was the first game he had started since September 2008, but it proved to be his last for the club as he limped off just five minutes into the game.
"I said, 'I think I've got a bit of a muscle problem here'," Hargreaves said.
"I was surprised it didn't go in the warm-up. I wasn't going to sprint, which sounds comical.
"I was just going to try to get through 45 minutes because that would have been a start.
"But I didn't even last five. I wasn't surprised because I had said to them that I had a hamstring problem, which I obviously did have."
Hargreaves, who was released by United in June, made his City debt on Wednesday, scoring in their 2-0 Carling Cup victory over Birmingham.
He revealed in March 2010 his concerns at some of the medical treatment he was receiving.
Asked whether he was unhappy with the treatment, Hargreaves replied: "Yes, absolutely you could say that. Not everybody's right.
"People make mistakes, that's part of life, and (when) it involves you, you're not too happy about it. Especially when, in the end, I miss almost two full seasons for Man United."