DENVER -- Just as the Nationals were beginning to experience life with a fully healthy lineup, Ryan Zimmerman headed back to the disabled list Wednesday with what has been deemed a "substantial" right hamstring strain.
Zimmerman will make his second appearance on the DL this season. He previously missed 44 games with a fractured right thumb.
"It's tough, but those are things that happen," Zimmerman said after the Nationals' 6-4 loss to the Rockies. "There's nothing you can really do about it. There's no reason to pout or feel sorry for yourself. I'm going to be here for these guys. We're playing good baseball. I think we'll continue to do that until I get back, and hopefully I'll get back sooner rather than later."
Just how soon Zimmerman could return is unknown. He will be out at least two weeks, but he didn't want to speculate outside of that timeframe.
"I wish I knew," Zimmerman said. "I don't want to say anything because I don't want to say something too long or too short. We haven't really had a chance to talk with the doctors at home yet. Once we talk to them, I think we'll have a better idea, but it's hard to say."
The Nationals recalled infielder Zach Walters from Triple-A Syracuse to take Zimmerman's spot on the roster.
Zimmerman suffered the injury while sprinting up the first-base line in the sixth inning of the Nationals' 7-4 win Tuesday. He grabbed at the back of his right leg just before tumbling over the bag.
"He's pretty sore today," Nationals manager Matt Williams said before Wednesday's game. "It's actually a little worse [than it was Tuesday night]. When I spoke with him this morning, he hadn't had any treatment on it. When you're hot and it happens, it doesn't feel as bad as it does the next morning."
Zimmerman's injury comes during perhaps his best stretch of the season. He was hitting .362 in July with six doubles and two home runs. The Nationals have been a far better team with Zimmerman in the lineup this season. When he starts, they are 33-19. When he doesn't play, the Nationals are 22-25.
"You don't ever want to see that happen to any of your teammates," Nationals first baseman Adam LaRoche said. "But a guy who has battled back from one injury and is a core piece of your lineup, that stings a little more."
Still, Zimmerman believes the first-place Nationals have the depth necessary to weather the storm until he returns.
"We're very fortunate to have a lot of good players on this team," he said. "Danny [Espinosa] played a lot this series and hit well. He's great at second base. Anthony [Rendon] showed how good of a third baseman he could be when I was out before."
Zimmerman was set to fly with the team to Cincinnati after the Nationals concluded their three-game series in Colorado, before returning to Washington for treatment. The Nationals have an off-day Thursday.
Walters, who is making his second trip up to the Major Leagues this season, has been sizzling of late. In his last 10 games at Syracuse, Walters hit .475. Through 60 games at Triple-A, he has hit 15 home runs with 48 RBIs.
In his first big league stint this this season (27 games), Walters hit .182 (6-for-33) with three home runs. His two-out, pinch-hit single in the ninth inning Wednesday helped the Nationals begin a two-run rally that nearly evolved into a comeback victory.
Walter's versatility in the infield made him the right choice to return to the Nationals, Williams said.
"When we sent Zach down from the big leagues last time, the instructions were for him to play second base, shortstop and third base," the manager said. "He's been doing a lot of that. He's swinging that bat really well. We want to get him reps, certainly."
Nick Kosmider is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.