By Curtis Pashelka

The Mercury News

OAKLAND, Calif. — The Oakland A’s have been plugging holes in their starting rotation since the tail end of the Cactus League schedule in March. If one pitcher went down, almost invariably, another came in to effectively fill the void.

But as injuries to starters continue to pile up, will there ever be a breaking point?

Thursday, with Sean Manaea and Brett Anderson now out for an indefinite period, the A’s turned to Frankie Montas against the Seattle Mariners, and it was a rough go.

The A’s allowed five runs in the first inning, three unearned, and lost 7-1 before a paltry crowd of 10,844 at the Coliseum to start a 10-game homestand. Montas went six innings, allowing four earned runs.

Montas, officially recalled by the A’s on Thursday, went 5-3 with a 3.75 ERA in two previous stints for Oakland earlier this season. But against Seattle, he threw 37 pitches in the first inning as the A’s dug a hole they couldn’t escape.

Montas allowed three hits and two walks to fall behind 2-0, two more runs scored after a Matt Chapman throwing error, and the Mariners finished off the inning with an RBI infield single from Dee Gordon to take a 5-0 lead.

The A’s couldn’t muster much in response, managing just three hits in seven innings off Seattle starter Wade LeBlanc.

While it’s possible the A’s could add a pitcher by Friday night’s MLB waiver trade deadline, or bring up another arm from Nashville in September when rosters expand, Montas, for now, is in line to start again during next week’s series against the New York Yankees. Daniel Mengden will start Saturday against Seattle.

Meanwhile, the latest news on Manaea and Anderson was not encouraging.

Manaea is out with rotator cuff tendonitis and A’s manager Bob Melvin labeled his chances of returning this season at less than 50 percent.

Anderson, meanwhile, has been diagnosed with irritation of the ulnar nerve in his forearm, and was scheduled to meet with doctors Thursday night, according to Melvin, to determine the next course of action. Anderson was initially diagnosed with a strained left forearm.

With the A’s having 13 pitchers start games this season, Melvin was asked if he feels snake bitten.

“It’s happened kind of in waves since spring training, so, at this point, not really,” Melvin said. “You expect some injuries, maybe not as many as we’ve had.

“Obviously the Manaea situation, with a guy that’s been basically our ace the entire season, stings a little bit more. Not that any of these don’t hurt. But if you sit around and feel sorry for yourself and think you’re snake bit, then it’s a distraction you don’t need.

“We do have some guys that have been productive for us this year in Montas and Mengden. It’s their time to step up.”

Manaea said Thursday he felt sore Aug. 25, a day after he threw five innings against Minnesota, when he was playing catch. He played catch again the following day, and the soreness lingered —which he added is unusual for him.

“I’ve been sore there before, but this is, I guess, a little more intense,” he said. “It’s not like it got any better. Usually after day two, it calms down a bit.”

Manaea, who is on a dose pack right now, hasn’t ruled out a return next month.

“It’s super frustrating,” Manaea said. “I feel like I’m letting everyone down. It really, really sucks that it has to happen right now. But there’s nothing I can do about it except try to get healthy and hopefully help this team by the end of the season.”

—With Montas and reliever J.B. Wendelken brought up from Triple-A Nashville, the A’s sent back down reliever Ryan Dull and outfielder Nick Martini.

In 15 games after he was recalled July 7, Martini hit .394. He struggled at the plate lately, though, going 12-for-58 (.207) over his previous 19 games. Dull, who was recalled from the Sounds on Tuesday, threw two shutout innings for the A’s in their 5-4 loss to Houston on Wednesday. Martini and Dull should be back after rosters expand in September, Melvin said.

—Melvin said Andrew Triggs, on the disabled list with right arm nerve irritation since May 18, will start a rehab assignment in the near future. Melvin said there was nothing imminent for Paul Blackburn (right elbow lateral epicondylitis). Blackburn, who has missed 46 games, said Thursday afternoon that he’ll throw a 30-pitc