Manchester United boss Sir Alex Ferguson has concerns over defender Nemanja Vidic.

The News of the World says Ferguson is concerned because the volatile Vidic is becoming increasingly irritable, taking out his frustrations in training-ground tackles on junior players.

Federico Macheda and Danny Welbeck have been on the end of some crude challenges recently, part of an ongoing problem with Vidic identified in training.

Vidic's form has also dipped. He was sent off against Liverpool for the third successive game last month and returned to the team yesterday only because of injuries.