Sir Alex Ferguson thinks it will be a major disruption to Rio Ferdinand's training regime if the Manchester United defender does answer England's call.
Ferdinand was selected by Roy Hodgson for the first time when the Three Lions boss unveiled his squad for the World Cup double-header with San Marino and Montenegro.
Yet the move has just created more rancour as Ferguson is evidently uncertain whether the 34-year-old should be reporting for duty in Burton on Monday evening. "The issue is not the amount of games, the issue is his whole preparation for football," said Ferguson.
"It involves treatment, it involves rest, it involves heavy days followed by some light days followed by some easy days.
"Our medical staff and fitness lads have done a great job with him. Because he hasn't been playing when the international breaks have come along we have detailed all the things he has to do, therefore it is a disruption to his normal preparation."
With Ferdinand's contract due to expire at the end of the season, there has to be a chance that, if the defender elects to resume an 81-cap international career two years since his last England appearance, Ferguson will choose not to offer him an extension to his present deal.
However, the United boss accepts the final decision lies with Ferdinand, who could face Reading in the Premier League at Old Trafford on Saturday evening.
"I was quite surprised when Roy Hodgson phoned me to say what he had done and I did say to him that I will talk to Rio," said Ferguson. "Of course it is a concern and I will need to speak to our doctor because we prepare Rio in certain ways.
"We have given him the treatments he needs for the various complaints he has in terms of his back and groin. So far it's worked very well. Rio has been absolutely magnificent for us.
"He has to make sure he's going to be okay in terms of the number of games he plays because what he is enjoying is how we plan for him. That has allowed him to reach his best performance level for quite a few years."