OAKLAND -- A's rookie starter Jharel Cotton threw a bullpen session Sunday morning, a sign of progression from issues with a blister on his right thumb that has hampered him for the past month.
While the A's previously thought Cotton might be ready to start Tuesday, instead they'll send Cotton to Triple-A Nashville for a rehab outing Wednesday, and Chris Smith will get the nod Tuesday against the Rays. It will be Smith's second Major League start; the 36-year-old went six innings but didn't get a decision July 8 in Seattle, allowing three runs on six hits in a 4-3 A's win.
Cotton will pitch after Kendall Graveman completes his rehab start, which is expected to be three innings and around 45 pitches. Manager Bob Melvin was pleased with Cotton's bullpen session and said he will throw about 65 pitches with the Sounds in Iowa on Wednesday.
"He threw without anything covering it today. Unless he's having a problem with it tomorrow, we feel like we're past that and it'll be Wednesday," Melvin said. "If he feels good and all goes well with that, we'll get him back and fit him into the rotation."
Cotton first felt the blister on June 23 in Chicago, getting pulled in the sixth inning vs. the White Sox because of it. After twice getting pushed back, Cotton faced the White Sox again July 3, going five innings, then was placed on the disabled list.
Castro has gone 3-5 with a 3.32 ERA in 38 innings with the Sounds this year. The 29-year-old reliever has had two previous stints in the Majors, pitching a combined 17 innings with the White Sox in 2014 and the Rockies in 2015. Melvin said that Castro could help in the late innings while Treinen makes his way to Oakland, and Castro pitched the ninth inning of the A's 7-3 win Sunday.
"We were really impressed by him in Spring Training, not only the performance he gave, but the enthusiasm," Melvin said. "He's excited to be back in the big leagues, and we'll see how it goes."
• Chad Pinder (left hamstring strain) took Sunday off after running the bases Saturday, but Melvin said Pinder will do a full complement of baseball activity Monday, after which the team could send him on a rehab assignment.
Alex Simon is a reporter for MLB.com based in the Bay Area. Follow him on Twitter at @alexsimon99. This story was not subject to the approval of Major League Baseball or its clubs.