Andy O'Brien is in danger of missing Leeds United's game against Championship leaders QPR with the thigh strain which ruled him out of Saturday's victory at Burnley.
O'Brien dropped out of United's line-up for the first time in eight matches after suffering an injury in training last week, and the centre-back is a major doubt for this weekend's high-profile clash at Elland Road.
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Boss Simon Grayson said it would be "a bonus" if O'Brien was passed fit for QPR's visit to Leeds but insisted the injury was not serious or likely to rule him out of a substantial part of the Christmas period.
Grayson reverted to a centre-back pairing of Neill Collins and Alex Bruce at Turf Moor, where United recovered from two goals down to earn a 3-2 win, and that partnership is likely to remain intact for the
length of O'Brien's absence.
Leeds are already without centre-backs Richard Naylor and Patrick Kisnorbo, both of whom are recovering from surgery on knee and Achilles injuries respectively.
"Andy got a thigh strain in the early part of last week," Grayson said. "We kept it quiet but he had to miss the game.
"It's nothing too serious. If he's back for this weekend then it's a bonus. If not, we'll analyse him for the week after."
O'Brien has been an influential figure since joining United on loan from Bolton Wanderers on October 29, and Leeds moved to agree an extension to his deal late last month. Bruce was at fault for Burnley's second goal on Saturday but Grayson was satisfied with the performance of his defence during a frantic second-half fightback.
Grayson said: "Andy's done really well for us but I thought Neill and Alex were fine once they got to grips with the game.
"They haven't played together for a while and I thought they defended well in the second half against a pretty potent strikeforce."
QPR suffered their first league defeat of the season last week, losing 3-1 at home to Watford on Friday night, and Leeds trail Neil Warnock's squad by six points after their success at Turf Moor.
United were 13 adrift of QPR in October but eight matches without defeat have elevated the club to within touching distance of the Championship's leaders, who hold a game in hand.
Grayson said: "There's a long way to go and I just want us to keep extending this run.
"We've got a very difficult game against QPR now and ultimately all that matters is where you are in April or May. We'll see where this takes us."