"I came here to help him, help him develop his career, and we haven't been able to do that," said Gase, who is 7-20 and has presided over the NFL's worst offense for the better part of two seasons.
His comments might seem obvious, considering the team's profound struggles, but they're noteworthy because Gase always has spoken of Darnold's progress in an optimistic fashion. His assessment comes with five games left in the season, after which the coach likely will be fired.
Gase said he hopes Darnold can finish on an upswing.
"That's why every game is so important," he said. "Keep trying to help him grow, keep trying to help him develop and see things the way he needs to see them and play the way I've seen him play in certain games."
Gase made it clear he's not blaming Darnold for the historically bad season (0-11), saying every position has contributed to the problems.
"We need to do things well around him, but at the same time, it's on me to get him to play better than what he's played," Gase said. "I haven't done a good enough job."
Darnold, speaking to reporters after practice, took accountability when asked about Gase's comments.
"First of all, I take full responsibility for the way I've played," he said. "I haven't played well enough. Like I continue to say every single week, we have great people in this organization. With that being said, everyone is going to take blame for certain part of us losing.
"But for me, personally, I've got to play better and put the team in the right position to have a chance to win games and make it close at the end."
Darnold is 0-7 this season (he missed four games with a shoulder injury) and has engineered only six touchdown drives. He's the lowest-rated passer in the NFL, with a career-low 64.0 rating. He has gone four straight games without a touchdown pass, the longest drought for a Jets quarterback since Geno Smith in 2013.
"Yeah, it's frustrating," Gase said of the touchdown drought. "For him personally, I'm sure he's bothered by it, knowing things like that.
"I look at it as we've got to do a better job as a staff. We've got to put these guys in the best position possible, and those guys have to go execute. It's on all of us. We have to find a way to do a better job. We have to find a way to put the ball in the end zone."
His future is a major question. The Jets likely will have the first or second pick in the 2021 NFL draft, and they could have a choice between Clemson's Trevor Lawrence and Ohio State's Justin Fields, the presumptive top two picks.
If general manager Joe Douglas decides to draft one of them, he will look to trade Darnold, who has one year remaining on his rookie contract. The amount of his fifth-year option for 2022 is expected to be about $25 million, fully guaranteed -- a seemingly prohibitive salary.
"This kid is the most mentally tough kid I've ever been around," offensive coordinator Dowell Loggains said. "There's going to be a really bright future for Sam Darnold."