Knee ligament operation. Will/can they get Zarate back? Probably not if they have a full 25 man squad.
I think it's more difficult to get a player out of part season (rather than x month) loan. To be honest, I think Zarate is just Taraabt with a higher scoring name in scrabble.
After they somehow got £60 million for Torres, I think Liverpool were playing with silly money when they replaced him and bought Carroll in for £35 million - they probably thought they had a real deal with a half price striker. Mike Ashley must have beaming at his balance sheet that financial year.
To be fair Carroll is a really good striker, he just won't have a great career because he's made of glass.
They don't have a full 25 man squad, but it's irrelevent, he's on a long term loan (it's the only kind PL clubs can sign a player on except in extreme circumstances) so they can't get him back unless they end up with so many players injured that they're unable to name 3 subs.