The outside linebacker was injured during a Ravens running play in the third quarter on Thursday, and reports have suggested his season could be over after initial examinations.
Speaking after the Bucs suffered a fifth loss in their last six games, Bowles said of Barrett: "He has an Achilles right now, so we'll wait for the MRI, but it doesn't look good."
Any significant absence for the two-time Pro Bowler would represent a considerable blow for the Bucs, who were already coping with several injuries ahead of Thursday's game.
Barrett has led the team for sacks in two of the last three seasons, and has recorded eight sacks and 43 tackles in his eight starts this campaign.
With Tampa Bay slumping to a 3-5 record despite winning their first two games of the season, Bowles acknowledges things are "dark" for his team, but he remains confident they can change their fortunes.
"It's still dark; until you win ball games consistently and play for four quarters consistently it's going to be dark," he said.
"That doesn't mean we can't get out of it, we just have a lot of work to do as coaches and as players."
The Ravens looked to have suffered an injury blow of their own when tight end Mark Andrews was ruled out with a shoulder injury in the second quarter, while wide receiver Rashod Bateman also exited with a foot problem.
However, head coach John Harbaugh played down any concerns over the duo after the win, saying: "They are not serious.
"Rashod was a tweak of what he had before, and Mark is not a serious long-term injury."