The Times says the Bulgarian is believed to be unhappy with the rotation system that Martin Jol intends to implement for his strikers this season. And there is a suspicion that Berbatov may have been unsettled by the speculation linking him with a £20 million move to Old Trafford - particularly as he has suffered least in Jol's policy of switching his front men.
United made a big play for Berbatov at the start of the summer, but were told he was not for sale. Since then, Sir Alex Ferguson has seen his forward line struggle to score goals while Wayne Rooney has suffered a foot injury. The club would ideally do business even before the match at home to Tottenham on Sunday.