Brian Griese replaced Garcia in a 13-10 loss to the Falcons, completing 26-of-37 passes for 269 yards and one touchdown.
Asked at his weekly news conference who would start against the Chargers, Gruden said: "We'll make that decision Wednesday.
"I think Brian did some very good things [against Atlanta]," Gruden added.
Garcia started the first game of the season but was replaced by Griese for the next four games before Griese was injured against the Denver Broncos on Oct. 15.
The loss to Atlanta dropped Tampa Bay to 9-5 and into the sixth and final place for a playoff spot in the NFC with two games left.
"We've got to win," Gruden said of Sunday's home game.
San Diego is 6-8 but still has a chance to make the playoffs.