Former Manchester United defender Paul McGrath says succeeding Sir Alex Ferguson is the "impossible job".

McGrath was sold to Aston Villa by Ferguson.

"No matter who comes in it's impossible to emulate Sir Alex Ferguson," he told talkSPORT. "It can't be done in modern day football.

"He's made them the top world football team and the respect around the globe that Man United has built is down to Sir Alex Ferguson. It's a sad loss for football."