WASHINGTON -- Following Wednesday's 3-1 victory over the Mets, the Nationals placed right-hander Jordan Zimmermann on the 15-day disabled list, retroactive to July 19, because of right elbow discomfort and recalled right-hander Collin Balester from Triple-A Syracuse.

Zimmermann was scheduled to pitch against the Cardinals on Thursday but Balester will get the nod instead. Balester, 23, went 6-4 with a 3.38 ERA in his last 12 starts with Syracuse. Over that period he posted 41 strikeouts and a .274 opponent's batting average in 69 1/3 innings. Overall, he went 7-9 with a 4.35 ERA in 19 starts.

Zimmermann started feeling pain during his last start, against the Cubs on Saturday. When he again felt pain after a bullpen session on Tuesday, the Nationals decided to shut him down for three or four weeks. The hope is that he will be ready for a rehab assignment at that time.

"I'm not really concerned at all," Zimmermann said. "I'm going to give it a little rest here and come back. I'll have one rehab start and be ready to go."

Once Zimmermann returns, he is expected to pitch the rest of the season, according to acting general manager Mike Rizzo. The original plan was to shut him down sometime in August.

"Zim could pitch tomorrow if he had to pitch," Rizzo said. "Instead of sending him out there against the Cardinals and have him pitch in a stressful situation, we are going to be cautious and shut him down.

"He is one of our prize prospects, and we are not going to do anything crazy with him. Like we handle all of our pitchers, like [Ross] Detwiler, [Shairon] Martis, Craig Stammen, [John] Lannan and Zimmermann, we are going to be very careful with them and look out for their best interests long-term, not [with the] short-term goals of winning a game."

Zimmermann, 23, is 3-5 with a 4.63 ERA in 16 starts this season. He is among the National League rookie leaders in strikeouts, starts, innings and wins.

Pitching matchup
WSH: RHP Collin Balester (0-0, 0.00 ERA)
Rated the top prospect in the Nationals organization by Baseball America entering the 2007 season, Balester went 3-7 with a 5.51 ERA in 15 starts with Washington last season.

STL: RHP Adam Wainwright (10-6, 3.01 ERA)
Wainwright was a tough-luck loser on Saturday night, when he gave up two runs and five hits in seven innings but fell to Arizona ace Dan Haren. Wainwright pitched well, giving up his first run on a bloop single to center and his second on a wind-aided home run to the right-field corner. The workhorse has gone at least seven innings in five consecutive starts, and the Cardinals are 3-2 in that span. He has not faced Washington this year.

Tidbits
Mike MacDougal has six saves in as many chances. ... Josh Willingham is hitting .297 with 13 home runs and 29 RBIs this season. ... Adam Dunn leads the Nationals in home runs (24) and RBIs (65).

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Up next
• Friday: Nationals (Garrett Mock, 0-3, 7.71) vs. Padres (Mat Latos, 0-1, 4.50), 7:05 p.m. ET
• Saturday: Nationals (J.D. Martin, 0-1, 11.25) vs. Padres (Tim Stauffer, 0-1, 2.08), 7:05 p.m. ET
• Sunday: Nationals (TBD) vs. Padres (TBD), 1:35 p.m. ET