Oakland, Calif. — The Tigers couldn’t be sure Friday if they were looking at a potential glut of starting pitchers, or a paucity.

It depended upon so many things.

Jordan Zimmermann’s bullpen session scheduled for Sunday at Oakland Coliseum will decide if he can rejoin the Tigers rotation or need to be shifted to the disabled list.

Then, too, there is Shane Greene’s recovery from a finger blister and a rehabilitation stint in the minors that has yet to prove whether he can be trusted to pitch long innings, or perhaps be limited to shorter bullpen stints.

There was also the matter of how rookies fit into the picture. Michael Fulmer was expected to see his stock move in one direction or another Friday as the Tigers got ready for an evening game against the A’s in the opening act of a six-game California road trip.

Another of the Tigers’ “kid” starters, Matt Boyd, also was expected to reveal Saturday if his steady work at Triple A Toledo has moved him closer to regular rotation work in Detroit.

Any or all of the above could prod the Tigers to ponder other moves as they try to stabilize a rotation that has had its issues, particularly with respect to Mike Pelfrey and Anibal Sanchez.

Zimmermann is fighting a strained groin that knocked him from this weekend’s start and led to Boyd’s call-up from Toledo. He has been working out and making progress. But neither the Tigers nor Zimmermann can exclude a trip to the disabled list, which, apart from missing a year with Tommy John surgery, would be a first experience for Zimmermann.

“It seems like everything’s going in the right direction, but the big test will be Sunday, when I have to push off,” Zimmermann said Friday, explaining the strain, until it began to improve, felt “like a really bad cramp.”

Gene Lamont agreed that Sunday’s test would be all-revealing. Lamont spoke in the visiting manager’s office, where he was filling in for Brad Ausmus, who has missed two games this week in the aftermath of his mother’s death, as well as his daughter’s high school graduation.

“If he can’t (make his next start), he’ll probably have to go on the DL,” Lamont said as the Tigers prepared for any number of scenarios and contingencies spurred not only by Zimmermann’s status, but also by Greene’s.

Greene was relatively strong in a Wednesday start for Triple A Toledo, striking out seven in 31/3 innings of scoreless work in which he was rapped for four hits.

But because Greene threw only 61 pitches, he likely needs at least another, longer start for Toledo if the Tigers want him as a rotation option. The problem there is the issue that put him on the DL last month: a finger blister that could recur if he is asked to throw too many pitches too soon.

“We’ve got to decide what we’re gonna do with him,” Lamont said. “Is he a starter or a reliever?

“We should know in a couple of days.”

Lamont was pleased the Tigers — for now — appeared to have options in the presence of two rookies, Fulmer and Boyd, both of whom arrived in deadline trades last July. Fulmer awakened Friday with a 3-1 record since he began filling in for Greene.

Boyd made eight starts for the Mud Hens and became the obvious option when Zimmermann’s groin put him on the shelf. He had a 2.06 ERA and a 1.15 WHIP, as well as a .232 opposing batting average.

He struck out 41 batters in 48 innings, walked 13, and allowed 42 hits. He throws four pitches and found that all four — fastball, slider, curve, change-up — were behaving during his time at Toledo, which was interspersed by a relief stint in Detroit during which he worked a 4 2/3-inning shift (no runs charged to him) against the Rangers.

“Every outing,” Boyd said Friday, “I was getting a little bit better.”