Matt Barnes, right, is still among the AL leaders in saves this season with 24, even though his last save was on Aug. 4. Charles Krupa/Associated Press

BOSTON — It’s no certainty that All-Star Matt Barnes will make the Boston Red Sox’s postseason roster.

Barnes dominated the first three months this season. He posted a 2.57 ERA in 35 outings. He struck out 45.4% of the batters he faced.

But he has a 6.75 ERA in 21 games since then going into Friday’s game against the Yankees. He has struck out 27.3% of the batters he has faced during that stretch.

Barnes has made two appearances since returning from the COVID-related IL. He has allowed one run, two hits and three walks while striking out two in 1⅓ innings. Only eight of his 21 pitches went for strikes while he recorded just one out vs. the Mets on Wednesday.

“We’ve got to keep working with him,” Red Sox Manager Alex Cora said Friday. “Obviously, there’s a few things he needs to get better, starting with pounding the strike zone. That’s something he did early in the season.”

Cora pointed out that Barnes’ velocity is down. Barnes topped out at 95.5 mph Wednesday, but he had a minimum fastball of 92.4 mph and averaged 94.0 mph, per Baseball Savant. His fastball has averaged 95.9 mph this season.

“Hopefully, we can get him back on track, because we do believe that obviously when he’s right, he’s one of the best relievers in the big leagues,” Cora said.

Time is running out this season, however.

Cora was asked how much he thinks Barnes’ struggles are mental compared to physical.

“That’s a good question,” Cora said. “I don’t know. I think velocity has to do with it. We saw a few 92, 93 in the last one. The gap between his fastball and obviously his offspeed pitches is not as big as early in the season. But we’ll keep working with him. He has a few things that he feels mechanically he’s not there yet. But at the end of the day, I think he needs to get back to being aggressive. Be aggressive in the strike zone. Be ahead in the count. If he can do that, he’ll be back. I cannot tell you if it’s mental. But one thing for sure, attacking guys was a big part of what he was doing early in the season and he’s not doing that right now.”