Gage was carted off the practice field in Florham Park, New Jersey, with the injury. He was in tears as he was leaving the field, with teammates taking a knee around him.
"We hear it's going to be pretty serious, and I'll wait to hear the final results," coach Todd Bowles said after the practice.
Gage's injury was noncontact, sustained while he was backpedaling during 7-on-7 drills.
"I can tell by the way that he was sitting on the truck that it was probably something that happened pretty bad," Bowles said. "Our hearts go out to him, and we'll see how it goes."
Injuries have plagued Gage's time with the Buccaneers. He was dealing with a hamstring strain all spring and early in training camp but had been fully practicing for over a week.
Gage, 27, took a pay cut this offseason to remain with the team.
He caught 51 passes for 426 yards and a career-high five touchdowns in 13 games (four starts) in his first season with the Buccaneers in 2022. Gage left the Buccaneers' wild-card game against the Dallas Cowboys on a stretcher and was taken to the hospital with a concussion, an injury that took about three weeks to recover from.
Gage is listed as a starter on Tampa Bay's depth chart, along with Mike Evans and Chris Godwin. His absence would give more playing time to Trey Palmer, Deven Thompkins and David Moore, among other wide receivers on the roster.
ESPN's Jenna Laine and Reuters contributed to this report.