That was nine days ago. Zimmermann was scratched from his next scheduled start, Tuesday against the Reds, with mild soreness in his right elbow.
Saturday, the Major League rookie leader in strikeouts (54) will return to action against the Rays at Tropicana Field.
"He threw a side [session Thursday], and everything's fine," said Nationals manager Manny Acta. "He's good to go."
Zimmermann, 23, first felt the soreness during his side session following his loss to the Giants. He said Friday that his elbow was better.
"I just needed a couple more days off and they moved me to the back end of the rotation. My arm feels good," Zimmermann said. "I just got a couple of days rest and the bullpen [session] was real light -- 15-20 pitches. [It was to] just to get on the mound and throw a little bit."
With 52 innings, Zimmermann already is one inning shy of his total workload in his first professional season, when he went 5-2 with a 2.38 ERA for Class A Vermont of the New York-Penn League in 2006.
He doubled his innings last year with 106 2/3 between Double-A Harrisburg and Single-A Potomac.
With four rookies and one second-year pitcher in the rotation, the Nationals will try to pick their spots to give the starters rest. Zimmermann's elbow soreness, which the team said is not serious, provided an opportunity to give him a few extra days off.
Zimmermann came into this season as Washington's No. 1 prospect, according to Baseball America. While he hasn't earned a victory since winning his first two starts in April, he has shown signs of the ability that prompted the Nationals to make him their second-round Draft pick (67th overall) out of the University of Wisconsin-Stevens Point in 2007.
Zimmermann has lasted six or more innings in five of his nine starts and hasn't pitched fewer than five in the other four.
And, Zimmermann said, he doesn't anticipate the change in his routine affecting his ability to record outs.
"I've been through some situations where I was on a five-day routine, then I was on a seven-day routine, then back on a five-day," Zimmermann said. "In college, I was on a seven-day. It doesn't affect me that much. Just got to get ready and do the same things I would do if I was in a five-day."
WSH: RHP Jordan Zimmermann (2-3, 5.71 ERA)
Zimmermann comes into Saturday's start ranked seventh in the National League with 9.35 strikeouts per nine innings. He also is ranked 12th in walks per nine innings (2.42) and fifth in strikeout-to-walk ratio (3.86).
TB: RHP Andy Sonnanstine (4-6, 7.00 ERA)
Sonnanstine allowed five earned runs -- all of which came through four Yankees homers -- in taking his sixth loss of the season Monday night. The right-hander is a master of deception, employing an array of pitches that he can throw from all different angles. But he has learned to primarily use his fastball to setup the other pitches.
Relief pitcher Kip Wells (15-day disabled list, strained right adductor) is scheduled to pitch back-to-back games this weekend for the Class A Potomac as he continues his rehabilitation assignment. Wells pitched two innings Thursday for Potomac and had a rest day on Friday. ... Right-fielder Elijah Dukes hit a two-run double off Rays starter Matt Garza in the first inning Friday in his first plate appearance against his former team. The hit gave Dukes his first multiple RBI game since May 13. ... This is the franchise's first trip to Tropicana Field since the Montreal Expos played there in 2000. The last time the two franchises met was the 2001 season in Montreal. ... Dukes wasn't the only former Rays player in a Nationals uniform making a return trip to the Trop. Relievers Jesus Colome (2001-06) and Joe Beimel ('05) also played for Tampa Bay. In addition, Nationals radio voice Charlie Slowes called games for the Rays from 1998-2004.
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Sunday: Nationals (Ross Detwiler, 0-3, 5.06) at Rays (James Shields, 5-5, 3.36), 1:38 p.m. ET
Tuesday: Nationals (Shairon Martis, 5-1, 5.04) at Yankees (TBD), 7:05 p.m. ET