Rio Ferdinand and Jonny Evans will both miss tomorrow's Manchester derby at Old Trafford.
Ferdinand has not recovered from the calf injury he sustained in the warm-up ahead of Manchester United's shock defeat at Wolves last week.
Evans played in that game but missed Northern Ireland's hammering by Scotland on Wednesday with an ankle injury and is still sidelined.
"Rio Ferdinand got a calf injury last week. He will be out for a couple of weeks," confirmed Sir Alex Ferguson.
"Jonny Evans was injured in training with Northern Ireland. He is out so Chris Smalling will play. I am sure he will do well."
Ferdinand's absence places a doubt over his availability for the Champions League trip to Marseille on February 23.
Yet Ferguson insists the England captain's latest injury setback is not a major problem.
"It could have happened at any time," said Ferguson.
"It is not as if it is anything to do with his back. That was our main concern last year but his back has been fine.
"You have to remember Rio has been in first-team football since he was 17. It is a long time. He will pick up little strains, like a lot of players do.
"This is not a long-term thing. It is a couple of weeks."
And Ferguson is confident about Smalling's ability to handle the pressure of the biggest game of his fledgling Manchester United career.
"Chris has made excellent progress this season," said Ferguson.
"He got a bit of tightness in his back last Friday, which is why I used Jonny Evans as a substitute last week.
"We are very pleased with him. He has been outstanding since he came to the club.
"He has played a few games now. Of course, he lacks that big-game experience but in terms of the experience he has had, he has used it well and he has done well."Reuse content