Alcaraz's hamstring problem also puts his participation in the FA Cup final in doubt but Martinez has plenty of faith in Scotland international Caldwell.
"It is vitally important to have Gary back with all the experience he brings and he looked sharp and ready for the end of the season," said Martinez.
"Antolin had the scans and he has a bit of a tear in his hamstring, which is what we expected, but we got fortunate he stopped playing at the moment he did.
"We will treat him and see how quickly he will respond but it will take the best part of three weeks.
"Antolin was in a good form so the focus is to get him back before the end of the season.
"It has been one of those seasons which, for one reason or another, we have had a difficult time with certain injuries.
"Ivan Ramis had a cruciate ligament injury, Ben Watson broke his leg and Albert Crusat bruised a tendon in his knee.
"We need to get everyone fit and ready over the next few weeks because the demands are huge."
Midfielder Watson has not featured since breaking his leg against Liverpool in November, but he is closing in on a return after a recent outing for the reserves.
"Hopefully I'm not too far away. After a long-term injury you just want to be out there," he said.
"I think now it is down to the manager whether he wants to put me in or not. Everyone is going to be needed."