Franco di Santo's thumping effort on Saturday earned the Latics a deserved 1-1 draw at Fulham, having fallen behind to a superb Giorgos Karagounis strike on a cold afternoon in west London.
However, the gloss was taken off an impressive point by a serious injury suffered by Ramis, who was carried off on a stretcher off towards the end of the game.
Martinez, who has already signed Roger Espinoza and Angelo Henriquez this month, fears his countryman has suffered a cruciate ligament injury but plans to replace him from within.
"We are in the January window and we are still looking for one player," the Spaniard said.
"I don't think we are going to look for a centre-half because we still have Antolin Alcaraz to come back from injury and Roman Golobart has done really well in the cup.
"I think we will have to cope with it internally, but we'll still try to add one more face before the window closes."