Peterborough manager Darren Ferguson will have to wait until the end of the week before bringing in any defensive reinforcements on loan.
The Posh lost key centre-back Ryan Bennett to Norwich in the transfer window and, despite signing Shaun Brisley from Macclesfield, Ferguson is looking for more new faces in his backline.
As part of the deal that took Bennett to Carrow Road, United can take a player on loan from the Premier League club if they wish.
Meanwhile, chairman Darragh MacAnthony said on his Twitter page that the club were not bidding for Crawley centre-back Kyle McFadzean after having an approach rebuffed in January.
Ferguson admits he is waiting on Premier League clubs to decide if they can loan out any squad members and expects that to be decided once players have reported back from international duty.
"If it is going to happen it won't be until Thursday at the earliest," Ferguson told the Peterborough Evening Telegraph.
"It is a matter of waiting on a couple of internationals at the club we're dealing with getting through their games this week. But I'm not going to panic about it. Craig Alcock will be fit and can play at centre-back if required."
Meanwhile, Posh goalkeeper Paul Jones has revealed he wants to stay at the club when his deal expires this summer.
Jones, who has battled with Joe Lewis all season, is currently first-choice goalkeeper at London Road and he is focused on retaining his spot and extending his contract.
"I like it here. The club and supporters are great, we play in a good league and I'm settled," he said.
"At the moment I'm just focused on playing games and ensuring we survive in this division. I didn't sort my contract out until quite late on in the summer, so there is no rush as far as I'm concerned. My agent looks after that side of things so I don't have to and I'm sure there are talks going on."
Ferguson is keen to tie Jones down to a new deal, especially as he expects Lewis to leave in the summer when his contract also expires.
"Paul has not let us down all season and his attitude was outstanding while he was out of the team.
"We're in the process of negotiating a new contract and I have a meeting planned with his agent. I certainly want Paul here, he wants to be here and we're trying to get it done."