Sir Alex Ferguson estimates Rio Ferdinand will be out of action for two weeks after missing Manchester United's victory over Birmingham this afternoon.
However, the United boss has now put a timescale on the problem, which would make the 30-year-old a doubt for England's World Cup qualifier with Croatia on September 9.
"I would imagine Rio will be out for two weeks," said Ferguson.
"I wouldn't think he will play against Burnley next week," Ferguson, who was already without Nemanja Vidic, told Sky Sports. "I would think he is out for the next two or three games actually which is a bit of blow."
United's defensive worries were increased 15 minutes from time when Jonny Evans limped off and was replaced by Wes Brown.