Right-hander Tanner Roark, acquired just before Wednesday’s trade deadline from the Reds, is expected to make his A’s debut Sunday against the Cardinals, manager Bob Melvin said.

Daniel Mengden, who is 5-2 with a 4.85 ERA, was listed as the A’s probable starter for Sunday, but Melvin wouldn’t say if the righty would be bumped from the rotation for the long term.

Melvin said the team is still considering options, including moving a starter to the bullpen or sending one to Triple-A Las Vegas to make room for Roark, who was 6-7 with a 4.24 ERA and 108 strikeouts in 110 ⅓ innings for Cincinnati.

Piscotty on the mend: Stephen Piscotty, recovering from a sprained right knee, had seven hits in 19 at-bats through Wednesday during a rehab assignment with Triple-A Las Vegas. He is expected to rejoin the big club for the Saturday-Sunday series against the Cardinals.

On the injured list since June 30, Piscotty was hitting .242 with nine home runs and 34 RBIs before getting hurt. The right fielder played his first three big-league seasons for the Cardinals and drew a standing ovation from the crowd in his return to St. Louis last year.

Estrada update: Right-hander Marco Estrada, who has made only five starts and pitched just 23 ⅔ innings this season because of a lumbar strain, said he plans to make a second rehab start for Class A Stockton.

“He came in here for a reason, and that was to pitch, originally at the top of the rotation,” Melvin said. “He takes that personally. He wants to be out there. He’s gone through some significant stuff with his back, unfortunately, which has precluded him from getting out there, but he’s fighting to get back and try to help the team.

“It’s not like he has given up and said: ‘This year is a wash.’ He’s still trying to do it.”

Rusty Simmons is a San Francisco Chronicle staff writer.