Ballack was given reassurances over his future by Mourinho at the club's training ground yesterday, although the Chelsea manager remains furious at being denied the services of one of his key players at such a crucial stage of the season. The 30-year-old flew to Germany for surgery to remove a piece of chipped bone in his ankle without the club's permission on April 27, ruling him out of Chelsea's Champions League semi-final against Liverpool and the remainder of their Premiership fixtures.

Mourinho has finally accepted that an operation was necessary but his anger has moved on to his medical team, who initially judged that Ballack's injury was not serious after he was substituted 18 minutes into the goalless draw with Newcas-tle United on April 22. The Germany player insists that the injury was misdiagnosed by the club's doctors and that the responsibility lies with English, who has already clashed with Mourinho this season.

English was forced into making a public apology on the club's website for "providing misleading information" after initially ruling John Terry out of the Carling Cup final in February with an ankle injury that the club captain picked up in a Champions League tie against FC Porto four days earlier.

English will be all too aware of the fact that his predecessor, Dr Neil Frazer, was forced out of the club after a similar dispute over the fitness of Arjen Robben two years ago. Frazer resigned after a heated row with Mourinho in front of Chelsea's first-team squad after the doctor's decision to rule Robben out of the Carling Cup final against Liverpool.

Mourinho is notoriously demanding of his medical team, though he has enjoyed a largely successful relationship with English after he joined from UK Athletics in 2005. English shares a philosophy of pushing players during their rehabilitation and has helped return Ashley Cole, Wayne Bridge and Terry to the first-team squad with remarkable speed this season, although he could be made the scapegoat for the row over Ballack, who retains an outside chance of returning for the FA Cup final against United.

Such a prospect would hardly alarm Ferguson given his dismissive assessment of Chelsea's two superstars. "I was quite happy that they were signing those type of players because I felt they were going to concentrate on Europe," he said. "When I see them I see European players. I thought it was designed to get them the European Cup so I wasn't too concerned.

"I thought, 'I hope they can concentrate on that and leave the league to us.' That would have been very nice of them, but they challenged us all the way." Didier Drogba, though, gave Ferguson plenty of cause for concern. "All season I have been saying to myself: 'Will somebody please shoot Drog-ba?' " he joked.