United manager Simon Grayson says Monday's trip to Arsenal could prove a great opportunity for some his squad and he contends with a number of injury doubts ahead of the game.

Paddy Kisnorbo has now been ruled out for the rest of the season and he joins Alex Bruce, Tom Lees, Robert Snodgrass, Jonny Howson, Leigh Bromby, and Davide Somma on the absent list.

"As of Thursday morning I had two fit centre backs," said the boss, who also revealed that Darren O'Dea had played on Monday despite picking up a hip injury at Barnsley just 48 hours earlier.

"We'll see where we are with Tom Lees and take the right advice with him, following his head injury, and we'll see where we are with Alex.

"He did some running on Thursday morning, but at this stage he's a massive doubt.

"It's fair to say the Arsenal game could be a great opportunity for some players."

Youngster Zac Thompson played much of Monday's clash with Burnley at right-back after Bruce switched to centre-back, alongside O'Dea, in the absence of Kisnorbo.