CHICAGO — The Chicago Cubs placed catcher David Ross on the seven-day concussion disabled list Wednesday and designated veteran reliever Joel Peralta for assignment.

Cubs manager Joe Maddon also said it's uncertain if centre fielder Dexter Fowler will be recovered from his right hamstring strain in time to start in the All-Star Game.

The moves before Chicago's game against Cincinnati opened roster spots for two players. Right-hander Adam Warren was called up from Triple-A Iowa to make a spot start against the Reds, and utility player Tommy La Sa Stella was activated off the disabled list and started at third base.

Ross took a foul ball off his mask in Tuesday's loss to Cincinnati that Maddon said "got him pretty good."

The 40-year-old Peralta signed with Chicago on June 13 after being released by Seattle. The right-hander had a 9.00 ERA in five appearances that included a scoreless inning Tuesday that Maddon called his "best day."

"He really looked closer to normal. It's just a matter of what we need right now, and he understood that," Maddon said. "If he chooses to not continue to play, he is going to be a fabulous pitching coach or bullpen coach or some kind of coach."

Fowler, one of five Cubs voted as All-Star starters by fans, was eligible to come off the disabled list Monday. But Maddon said they hadn't decided whether he'll go on a rehab assignment later this week.

The All-Star Game, which would be the first for Fowler, is Tuesday.

"Of course there's motivation. He wants to play in the All-Star game," Maddon said. "Listen, don't anybody fault him for that. This is a once in a lifetime opportunity. Who knows if it's going to happen again and I'll all for it. . But the overriding concern is he plays for us the rest of the year."

La Stella, hitting .291, had been out since straining his right hamstring June 7.

Cubs slugger Kyle Schwarber also talked to reporters Wednesday, saying he's progressing well from season-ending surgery to repair torn ligaments in his left knee.

Schwarber, who has shed crutches, hopes to start jogging soon. He also expressed thanks to team president Theo Epstein for publicly refuting reports Schwarber could be traded for bullpen help.

"I want to stay here," Schwarber. "Obviously things are out of my control, but since he did say that, I take that to heart. It means a lot."