Sir Alex Ferguson admits Rio Ferdinand is doubtful for Manchester United's Grand Slam Sunday showdown with Liverpool.
Ferdinand is struggling with a back injury and sat out Wednesday's 2-0 home win over Bolton Wanderers which sent United three points clear at the top.
Gerard Pique started alongside Nemanja Vidic at centre-half, although the Serbian stopper was replaced after an hour after taking a whack to the nose.
United boss Ferguson is confident Vidic will be able to face Liverpool, but is concerned about Ferdinand's availability for Sunday's game, live on Sky Sports 1.
"Vidic was elbowed in the nose again and the bleeding wouldn't stop," Ferguson told Sky Sports. "Hopefully he'll be okay and will get sorted by Sunday.
"Rio Ferdinand is more doubtful, that's why I played Pique to find out his form and to give him the experience of playing because it gives us an alternative."
Defensive regulars Wes Brown and Patrice Evra started the Bolton victory on the bench, and Ferguson was keen to assess his options given the worries surrounding Ferdinand's fitness.
He added to MUTV: "We also wanted to rest Wes Brown in case Rio doesn't make it, then we've got the alternative of playing Wes at centre-back - that's a decision we'll have to make.
"We tried Owen Hargreaves at right-back, and we can play John O'Shea there on Sunday and bring Patrice Evra in. It's important to do these things tonight, simply because of Rio's injury."