SEATTLE -- The A’s are one step closer to returning their No. 1 starter from last season as left-hander Sean Manaea will begin a rehab assignment with Class A Advanced Stockton on Monday.

Manaea will pitch three innings as he builds up his strength to a Major League workload, and he’ll need multiple rehab starts to stretch out his arm, manager Bob Melvin said. But if all proceeds well, Manaea could be back with the A’s within a month as MLB rules limit pitchers’ rehab assignments to 30 days.

Manaea’s rehab from surgery he underwent last September on his pitching shoulder was stalled two weeks ago when he experienced pain in his left side. He was initially slated to begin a rehab assignment on June 25, but shut down his throwing program. He threw a 30-pitch bullpen session on Tuesday at the Coliseum.

“We have to get him up to where he's comfortable and performs well, but boy, it would be a nice shot in the arm for us to get him back,” Melvin said. “He's a very excitable young man. He loves to pitch and just loves to be with his team, so I know that this is the start of a process that was delayed a little bit by the side thing that he had, but he's always been intent on trying to give us a couple months this year. Hopefully that's the case.”

Jharel Cotton will also begin a rehab assignment with Stockton on Tuesday. When he returns, Cotton will likely contribute Major League innings in a bullpen role, as part of a plan to limit his innings after undergoing Tommy John surgery in March of 2018. Cotton also underwent right hamstring surgery on June 6 that stalled his rehab.

Canha scratched with back spasms

Outfielder Mark Canha was scratched on Saturday due to back spasms. If he’s unable to return on Sunday, Canha would be in line for six days rest, as the A’s don’t open the second half of the regular season until next Friday when they host the White Sox.

“One of the reasons we're keeping him out today is hopefully he'll be able to play tomorrow, but I'm not sure,” Melvin said.

Canha, who missed 12 games earlier this season with a sprained right wrist, is slashing .233/.374/.503 with 12 homers over 159 at-bats in 57 games. Jurickson Profar took Canha’s spot in the starting lineup, while Chad Pinder took Canha’s post by moving from left to right field.

Wendelken recalled, Blackburn optioned

The A’s announced on Saturday that they’ve recalled right-hander J.B. Wendelken from Triple-A Las Vegas and optioned righty Paul Blackburn back to Las Vegas.

Wendelken, a reliever, would’ve been recalled on Friday instead of Blackburn, a long-inning pitcher who was recalled one day prior, but Wendelken wasn’t eligible to return to the Major League roster until Saturday after being optioned on June 26. The A’s have a more pressing need for relief arms than starters, and Blackburn likely wouldn’t have seen much action unless the club needed him in a long-relief role.

“It was tough on Paul to come here, just be here for a day and have to leave, but J.B. is a reliever and Paul is more of a starter, and with the issues that we've had with starters, we need to have him down [at Triple-A] starting,” Melvin said.

Wendelken embarked on his third stint with the big league club, having gone 1-1 with a 4.94 ERA over 23 2/3 innings in 20 outings. He pitched two clean innings and recorded four strikeouts in Oakland's 6-3 loss on Saturday.

Wendelken will provide added depth to a bullpen that Melvin has leaned on heavily over the past week ahead of the All-Star break.

Also on Saturday, right-hander Aaron Brooks was claimed off waivers by the Orioles. Brooks had struggled to a 5.01 ERA over 50 1/3 innings across 15 outings, including six starts. Brooks was designated for assignment by Oakland on Wednesday.