The Latics have already signed forward Angelo Henriquez on loan from Manchester United and midfielder Roger Espinoza from Sporting Kansas City - but Martinez is not finished his recruitment drive.
The Spaniard did however rule out defensive reinforcements, despite fears centre-back Ivan Ramis may have suffered cruciate ligament damage.
Martinez said: "We are in the January window and we are still looking for one player.
"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."
Martinez also took time to heap praise on striker Franco di Santo, who responded to reported interest from Liverpool by lashing home the equaliser in Saturday's 1-1 draw at Fulham.
Martinez said of the Argentinian: "It was special. Strikers are always going to be judged on clinical finishes and what they do in front of goal.
"Franco deserves a special mention for the contribution he has given to the team against Fulham.
"To have a striker with the generosity in his work is difficult to find in the modern game and I was very pleased with the way he worked hard for the team.
"Then the way he found the back of the net was a special, special strike and I think it had to be that way with the home goalkeeper's form.
"Franco can, though, be that clinical finisher, with the right, the left and good in the air. He is a special, special striker and I am glad he got the reward for all the hard work he put in."