Both Ryan Zimmerman and Manager Jim Riggleman said they hope he can return to baseball activity within 10 days, which could probably get him back on the field some time around April 24, the first day Zimmerman will be able to come off the 15-day disabled list. Still, Zimmerman said he had “no clue” when he might return. As we reported yesterday, it would be a surprise to see Zimmerman back before three weeks.

“It’s frustrating,” Zimmerman said. “I think nobody every wants to go through it but the important thing is to get healthy. There’s a long season ahead so you don’t want to have to deal with something like this for six months.”

The Nationals will be cautious with Zimmerman, who is on the disabled list for the second time in his six-year career. Zimmerman first felt the strain in his abdominal muscle early in spring training. At the time, he called it “a non-facotr” and missed three games, from March 8 to 10. But it resurfaced at the start of the season and he severely strained it Saturday night, sliding into second base.

“We’re certainly not going to rush the process,” Riggleman said. “I thought we were very conservative in spring training when he was feeling this. We’ve just got to really let it get better. We cannot ask him to play at 80 percent. We’ve got to let the thing get really close to 100 percent.”

Zimmerman, one of the Nationals’ hardest offseason workers, called the injury “just kind of a freak thing that happens.” It is not related to the oblique injury that caused him to miss the final two weeks of the 2010 season.

“You really can’t do much for it,” Zimmerman said. “You just have to let it rest. It’s one of those where you use your ab muscles for everything during the day so the key for the first 4-5 days is to let it rest as much as you can and let it recover. After that you kind of evaluate and if it’s feeling better you can start strengthening and rehab stuff.”

With Zimmerman out of the lineup, the Nationals will use a combination of Michael Morse, Alex Cora and Jerry Hairston, tonight’s starter, at third base. Morse has never started a major league game at third base.

Also, Class AA Harrisburg placed catcher Derek Norris, widely regarded as one of the top 100 prospects in baseball, on the disabled list after he sprained his ankle last night.