Geren said on Saturday that Harden would have to throw a side session on Sunday in order to be ready for Tuesday.
When asked if he had started making backup plans in case Harden isn't ready for his next scheduled start, on Tuesday in Baltimore, Geren said it is still too soon to start worrying about that.
"We've got a couple of options," Geren said. "We've talked about a few different scenarios, but there's no need to get into that until we know."
Among the options potentially at Geren's disposal are Lenny DiNardo and Brad Halsey, who has pitched well with Triple-A Sacramento so far this season. Halsey has posted a 2-0 record with a 2.65 ERA and 17 strikeouts in 17 innings.
Geren pleased with Crosby's progress: Bobby Crosby appears to be getting past some lingering back troubles. The club has been keeping a close eye on Crosby's back since an injury ended the shortstop's season early last year. Crosby has missed one start so far this season.
"Crosby said he felt great," Geren said. "He's had some nice outings in a row, and that's good to see."
In recent weeks, there has been some concern about Crosby playing in a day game following a night game. Geren said Crosby was one of the first people he would talk to Sunday morning before setting his lineup. Coincidentally, while driving to the ballpark on Sunday morning, Geren pulled up next to Crosby at a red light, where Crosby said he felt fine. Crosby was in the lineup.
A's starters getting it done: Oakland is getting solid work from its starting pitchers. Joe Kennedy allowed just one run in his five innings on Saturday night, marking the eighth time this season an A's starter has surrendered only one run or fewer. It also was the 15th straight game in which the Oakland starter gave up three or fewer runs.
A's pitchers also are getting off to fast starts. Through the first 17 games this season, Oakland hurlers have not allowed a run in the first inning.
Up next: Right-hander Dan Haren (1-2, 1.44 ERA) will make his fifth start of the season Monday in Baltimore against Orioles left-hander Erik Bedard (3-1, 5.40 ERA). First pitch is set for 4:05 p.m. PT.
Shawn Smajstrla is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.