NORTH End go into possibly their toughest test of the season this weekend sweating over the fitness of skipper Sean Gregan.
After seeing his captain pick up a foot injury during the first half of Tuesday's 4-2 victory over Sheffield Wednesday, Moyes fears he may be forced into the transfer market again.
Michael Jackson and Colin Murdoch are both out injured at present, which has forced Gregan into the back four alongside Chris Lucketti.
But despite having youngster Paul Reid -- on loan from Rangers -- at his disposal for one of the centre-half positions, Moyes knows he will down to the bare bones this weekend.
Moyes said: "It is becoming worrying. We can laugh but I'm beginning to get worried.
"Sean took a knock on his foot and signalled that it was hurting and then when the physio looked at it you could visibly see the swelling through the boot.
"We are waiting for an X-ray and hopefully it won't be serious and we can have him available for Sunday.
"We've got an awful lot of big games coming up and I'll have to look and see whether we need to go into the market for another centre-half."
Since North End and Manchester City last met in October, the Maine Road outfit have established themselves as the favourites to win the league, toppling Burnley in the process.
But a defeat at the hands of Wimbledon last weekend has left boss Kevin Keegan threatening that he will shake things up ahead of Sunday's showdown.
He said: "Paulo Wanchope will come back against Preston. He will definitely play. I will find a place for him because he gives us a lift.
"I will have Steve Howey back and I will be tempted to play him if he proves his fitness. I will have Danny Tiatto back, too.
"Maybe we missed some of his drive on Sunday. He certainly would have shown a bit more commitment than some of them showed at Selhurst Park.
"We got what we deserved against Palace and if we keep playing like that for the rest of the season we will stay in the First Division."
For Moyes, the knowledge that Dickson Etuhu and Paul Reid have bedded in so quickly will be a boost -- as will the fact that David Healey, Jon Macken and Richard Cresswell have scored in the last fortnight.
Macken said: "I was pleased to get a goal on Tuesday.
"Hopefully now I can go and score a few more.
"I'm not sure about scoring the same kind of goal against City but I'd love to get a goal at Maine Road.
"It would be fantastic and we are capable of doing that as we proved this season already."
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