Newcastle United will assess injuries to both Siem De Jong and Moussa Sissoko, with the pair facing time in the treatment room.
De Jong, just back from a collapsed lung, suffered a knock in training and did not make the journey to Wales for the 2-0 loss to Swansea City.
And Sissoko injured his groin at the Liberty Stadium, leaving him a doubt for the trip to Manchester United.
McClaren said: “We lost a big player in Moussa. We don’t know the seriousness of it yet.”
If Sissoko does not make it back in time for the clash at Old Trafford, De Jong would be deemed as a replacement and McClaren did not seem concerned after the game.
McClaren said: “We think it is just a kick on the shin which flared up. He nearly made it (in time) but unfortunately didn’t (but) it should not be too bad.”