"I'm mad at myself that I let him go back in there in the second half," Gase said after the Jets fell 27-17 to the Buffalo Bills, according to ESPN's Rich Cimini.
Bell, who battled hamstring issues in training camp, was seen grabbing the back of his leg before halftime. He returned briefly in the third quarter with his hamstring wrapped, but was eventually removed and watched the rest of the game from the sideline.
"That play looked bad," Gase said of the first-half reception on which Bell got hurt. "I'm watching and I thought it was going to be a touchdown, then he got grabbed. And kind of the way he planted and torqued, it looked really bad.
"I saw him grab his hamstring and he wouldn't come out. We come in at halftime. I let him go back in there. I was worried about it, and we were eventually like, 'I can't put you in there. We can't take a chance on getting more hurt than you already are.'"
Gase and Bell clashed briefly in camp when the Jets pulled him out of practice due to hamstring tightness. Bell tweeted afterward that there "ain't nothin wrong with my hamstrings." In response, Gase questioned why Bell would air his frustrations on social media.
Bell took six carries for 14 yards in the Week 1 loss to Buffalo. The Jets will face the San Francisco 49ers in Week 2.