"We are trying to calm that down as much as we can today," Williams said.
It marks the second time in three games Zimmerman was not in the starting lineup because of an injury. He missed Sunday's game against the Braves because of a sore left foot.
Zimmerman has been Washington's hottest hitter. Entering Tuesday, Zimmerman was 22-for-56 [.393] with seven home runs and 25 RBIs.
"It's a tough one. He has been hotter than anybody, playing really well, helping us win games," Williams said. "It's unfortunate something like that would happen. We hope that it's just a tweak and he'll be ready to go -- hopefully -- tomorrow. Right now, we don't know that. So we'll try to calm it down as much as possible."
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All theTime. He also can be found on Twitter @WashingNats This story was not subject to the approval of Major League Baseball or its clubs.