James Paxton has been back with the Red Sox for less than a month, but he was high on the list of players they couldn’t afford to lose.

On Tuesday, manager Alex Cora admitted the veteran left-hander’s season could be over.

“We’ll see where we’re at in a few weeks, but just stay the course, you know, get the rehab going, and hopefully he can contribute,” Cora said. “But that looks like a long shot.”

Paxton, 35, exited his Sunday start after two-thirds of an inning and just five pitches to three total batters. Even with help from the coaching staff and trainers, he could barely walk off the mound. In the subsequent days, he’s hobbled around the clubhouse on crutches, a concerning sight before the Red Sox even had the official diagnosis: a partial tear of his right calf.

“I think right away, he had a pretty good idea what was going on,” Cora said.

The Red Sox first signed Paxton to a one-year deal with a two-year club option or, if declined by the team, a one-year player option ahead of the 2022 season, as he recovered from Tommy John. When he took the mound for his first rehab outing that mid-August, he suffered a Grade 2 lat tear, ending his season.

Paxton made his Red Sox debut on May 12, 2023, and pitched well for the club in the first half, earning American League Pitcher of the Month honors in June. He struggled in the second half, however, and right-knee inflammation officially ended his season in early September.

After becoming a free agent last fall, Paxton signed a one-year deal with the Dodgers. He made 18 starts for them, the last one against the Red Sox when they opened the second half of the season with a three-game set in Los Angeles. After the Dodgers designated Paxton for assignment the next day, the Red Sox traded for him.

The current plan is to slot Cooper Criswell back into the rotation when he comes off the COVID-related injured list, which could be as early as Friday. But without Paxton, the Red Sox rotation is back to being a righties-only operation. And with the trade deadline in the rearview mirror, there’s no real way to fix that.