Former Brazil star Ronaldo has hit back at Manchester United manager Sir Alex Ferguson for referring to him as "the fat one".

The Scotsman is thought to have made a comment regarding the 36-year-old's weight when he tried to distinguish between the ex-striker and Real Madrid star Cristiano Ronaldo ahead of United's exit from the Champions League on Tuesday.

"I have nothing to add on my old physical appearance," the Daily Mail quotes Ronaldo as saying. "I regret how disrespectful he was when he referred to me, it was not something that befits a 'Sir'."

Ronaldo, whose weight has fluctuated over the years, retired from the game in 2011.