Mickey Thomas is shocked by Wayne Rooney's attitude and says there is no better club for him than Manchester United.
Former United player Thomas was stunned by Sir Alex Ferguson's revelation on Tuesday that Rooney has suggested he has no intention of signing a new contract at Old Trafford and is keen to take on a fresh challenge elsewhere.
The England striker is yet to comment on the news, but Thomas says he is "mystified" as to why he would want to leave United.
"I'm shocked and the footballing world is as well, certainly if you're a Manchester United fan," he told Sky Sports News.
"I can't get my head around why he's come to this decision. He's at the biggest club in the world, he's come here to win trophies and he's done that.
"Although he's not playing too well and has had a few problems off the football pitch, everyone, including myself, will be mystified as to why he's come to this decision until he releases a statement."
Thomas insists Rooney's reasons might be financial - he could possibly earn more money elsewhere - because he says Manchester United is the perfect club for him.
He insists they have protected him since he arrived from Everton in 2004 and Ferguson is the best manager to look after his talents.
And despite his much-publicised off-the-field problems, Thomas says it would be a mistake for Rooney to move on.
"I think the majority of players these days go for financial reasons," he continued.
"United are always striving to be successful and to win trophies. They've got a great pedigree and he's been involved in that in the last few years.
"I don't think he can go anywhere better than Manchester United Football Club. The manager has given him all of the best advice and since he's walked through the door, Wayne Rooney has been protected from the media pressure.
"What went on off the pitch in the last few months, Sir Alex Ferguson couldn't control that, so you have to look at the player and say he's brought it on himself.
"If he wants to leave for that reason, to get away from the pressure, it's going to follow him. It's never going to go away from Wayne Rooney.
"Don't forget, he's been touted as the best player in the world. Everywhere he goes the pressure is going to be immense.
"There's only one man that can look after him and that man is Sir Alex Ferguson."
Thomas says he has been disappointed with Rooney's form since a below-par World Cup with England over the summer.
But he says the PFA Player of the Year will leave a gaping hole in Ferguson's squad if he leaves in January and his departure would make it difficult for United to challenge for trophies.
"He's come back this season and he hasn't performed like he did last season, which has been a huge disappointment for him and the Manchester United fans," he said.
"He's got to get back to his best and play football, but at the moment it's not working for Wayne Rooney. We know about his off-field problems. Those have been immense for him and maybe that's the reason he's come to the decision to leave this football club.
"For footballing ability, Wayne on his day is the best in the world, so it's going to be a massive problem to replace him if Wayne leaves in January.
"The ambitions are to win the Premier League back from Chelsea this season and with him not on board it's going to be very, very difficult."
Who is Wayne Rooney most likely to join?