The A's haven't determined replacements for Overton and starter Jesse Hahn, who was placed on the disabled list Friday with a strained right shoulder. Manager Bob Melvin said right-hander Zach Neal is an option if the team can avoid using him in long relief over the next three days, estimating Neal could throw as many as 80 pitches in a starting role.
"He's pitched with a lot of confidence," Melvin said. "His last two times out have been really good."
Neal hasn't allowed a run in three appearances since being recalled from Nashville on July 21. He's made one start with the A's this year, giving up seven runs in four innings on May 25 against the Mariners.
Cotton, the A's No. 16 prospect, according to MLBPipeline.com, allowed one run in six innings while striking out five in his Nashville debut Aug. 4., and he's in line to make his next start Tuesday. Oakland hasn't named a starter for either Tuesday or Wednesday's games against the Orioles.
Overton posted a 10.97 ERA in five starts, and he allowed 11 homers in the first 21 1/3 innings of his career. Melvin said Overton struggled with his command when falling behind in counts, and the skipper hopes a Triple-A stint will help Overton regain some of his confidence.
"He's trying, it just seems like every time he makes a mistake, it ends up a home run," Melvin said. "He has done some good things in Triple-A. I certainly don't think what we've seen is really who we have with him. At some point in time he'll get another opportunity here."
A's starters were unable to complete five innings in five of their past six games going into Sonny Gray's start Saturday. Schuster, who had a 15.43 ERA in four games entering Saturday, can provide long relief, as can Daniel Coulombe and Andrew Triggs. Coulombe and Triggs each threw at least two innings Friday night against the Cubs.
Oakland has two other healthy starting pitchers on its 40-man roster in Daniel Mengden, who was optioned to Triple-A on July 26, though Melvin said he would not be rushed back up, and Raul Alcantara, who is 2-0 with a 0.44 ERA in his past three starts.
• One starter the A's hoped would be a key part of the rotation, Henderson Alvarez, is getting closer to beginning a throwing program, Melvin said. Alvarez had shoulder surgery last July and has been shut down on two separate occasions this season following Minor League rehab starts.
• Melvin said the A's will approach Sean Doolittle's return cautiously as he recovers from a left shoulder injury. Doolittle threw a 25-pitch bullpen session, but when asked about when to expect the lefty's return, Melvin said it "won't be quickly."
Doolittle was encouraged with his recovery.
"When it's the second relatively significant injury I've had to my shoulder in two years, we have to make sure we're really thorough with the process," Doolittle said Friday.
Mark Chiarelli is a reporter for MLB.com based in the Bay Area. This story was not subject to the approval of Major League Baseball or its clubs.