The veteran right-hander injured his left Achilles covering first base in his last start, but will be ready to pitch Thursday against Jordan Zimmermann and the Nationals. The Reds starter said he was very sore on Saturday and Sunday, but had a good bullpen session on Tuesday.
"I felt surprisingly real good," Arroyo said. "I'm good. I just threw a regular bullpen, 45 pitches. It was a little shorter than I have been, but not because of my ankle. It was because it's getting late in the year and hot."
Arroyo has pitched at Nationals Park only once, and the outing came last season. He worked eight innings and gave up only two runs, but a blown save robbed him of a victory.
He's hoping for better luck this time around, and the Reds could use it. Cincinnati defeated the Nationals, 2-1, on Wednesday, but still trail the first-place Brewers by 12 1/2 games in the National League Central.
As for Zimmermann, he has struggled since the All-Star break after posting 11 consecutive quality starts before the midway point, and could be running out of pitching opportunities. He enters Thursday's matchup having pitched 145 innings this year -- his first full season back from Tommy John surgery -- and the club plans to limit him to 160 innings.
"He is really a strong young man," Nationals manager Davey Johnson said. "He is probably feeling better than anyone we have on our staff. If I didn't know the history about him, [shutting him down] would not be in my thought process."
Reds: Renteria out on Wednesday
Shortstop Edgar Renteria left Tuesday's game with a strained right groin and was out of the lineup Wednesday. He is listed as day to day. Paul Janish started in his place and went 1-for-3.
Nationals: Pudge plays catch
Catcher Ivan Rodriguez, on the disabled list with a right oblique strain, played catch on Wednesday and could be activated from the disabled list before the team expands its roster in September.
Ryan Zimmerman has reached base safely in 23 consecutive games. He went 2-for-4 with a home run on Wednesday.
The Nationals are 17-15 against the NL Central this season.
Reds starters have allowed 80 runs in the first inning this season.
Saturday's game between the Reds and the Pirates in Pittsburgh has been changed from 7:05 p.m. ET to 4:11 p.m. to accommodate a national FOX broadcast.
Cincinnati has 11 walk-off losses this season, the most in a season since 1993, when they lost 14 via a walk off.