Newcastle manager Alan Pardew would like to sign a defender in January, but knows he is not facing an easy task.
Wednesday night's 3-2 home defeat by West Brom left the Magpies without a win in six Premier League games amid injury and suspension problems.
Pardew was unable to call upon centre-back Steven Taylor, who is out for the season after surgery to repair his Achilles, and lost full-back Davide Santon to a knee problem, while Yohan Cabaye and Dan Gosling were both suspended.
A replacement for Taylor is a must in January and Newcastle have been linked with Ajax's £10million-rated Jan Vertonghen.
The impending losses of 13-goal striker Demba Ba and key midfielder Cheick Tiote to African Nations Cup duty with Senegal and Ivory Coast, respectively, will blow another hole in the manager's resources for several weeks.
Pardew was giving nothing away about his potential targets, but said: "We are having to look at our squad because we are stretched, especially defensively.
"We have made some calls to try to find out who is available, but it's a difficult window.
"You want to try to get a good player in a window when teams don't want to lose their good players, so it's not just difficult for us, it's difficult for every team.
"You locate a player, but then they have got to get a replacement and is another first-team going to let a replacement go? There's a knock-on effect.
"It's a difficult window. We will have to see how it pans out."
Pardew hopes to retain the services of Ba and Tiote until around 15th January, but the former in particular will be a huge miss when he does go.
Ba twice dragged Newcastle back into the defeat against West Brom with stunning equalisers and Pardew said: "He's a great player, and you are going to miss great players.
"He is going to the African Cup of Nations and he will probably want to win that. Knowing Demba and the way he is playing, he probably could. He has been absolutely terrific for us."