Wallace started but played less than 4 minutes in Thursday night's game before he became dizzy and asked to come out. He staggered to the bench and had to be assisted by his teammates before the Cavs' training staff stepped in.
Wallace underwent a series of tests at the Cleveland Clinic on Friday. The team said the defensive stopper could be upgraded but it was "best case, 50-50" that Wallace would play Saturday in Game 3.
Cavs coach Mike Brown said if Wallace can't go, Anderson Varejao would likely start up front alongside LeBron James and Zydrunas Ilgauskas as Cleveland tries to climb back from an 0-2 deficit in the best-of-seven series.
Wallace joined the Cavaliers in a trade from Chicago in February. He missed several regular-season games because of back spasms.