Manchester United boss Sir Alex Ferguson says Rio Ferdinand could miss the rest of the month with a thigh injury.
The England international suffered a blow in training on Friday, forcing him to miss United's season-opener against Birmingham.
Ferguson has confirmed Ferdinand is having a scan on Monday that will assess the severity of the knock.
"Ferdinand pulled a muscle in training on Friday afternoon," he told Sky Sports.
"He's out. I don't know how long he's going to be out.
"We're sending him for a scan on Monday."
Jonny Evans also suffered an injury during the 1-0 victory over Birmingham at Old Trafford on Sunday.
And, following the match, Ferguson told Sky Sports that Ferdinand may not figure again until after the clash with Arsenal on 29th August.
"I would think he's out for the next two or three games actually, so it's a bit of a blow," he said.
"Jonny Evans has had to come off today.
"In the last year or so, we've been having problems with defenders, one after another.
"Fortunately we've got stand-ins like Wes Brown today. He's not done much training but his experience counts when you bring him into a situation like today.
"We had [Ritchie] de Laet on the bench today and he'll probably figure now."