Medlen underwent Tommy John surgery in August 2010 and last started a Major League game on Aug. 4 of that year. He has appeared in 38 games out of the bullpen this season and has a 2.48 ERA in 54 1/3 innings.
Braves manager Fredi Gonzalez said that Medlen will be limited to between 65 and 75 pitches, but Medlen isn't dwelling on his pitch count.
"I just want to be effective and try to go as deep as I can with the pitch count I'm given," Medlen said. "I need to make them last."
Medlen's start comes in the wake of a rough season for Jair Jurrjens and Randall Delgado having been sent to Triple-A Gwinnett after the All-Star break.
Right-hander Ricky Nolasco will toe the rubber for the Marlins. Although he has averaged 7.1 strikeouts per nine innings against the Braves in his career, Atlanta has had his number this season.
In two starts against the Braves, Nolasco is 0-2 with a 9.64 ERA. He last faced Atlanta on Wednesday at Marlins Park, and exited after allowing six runs on eight hits over 5 1/3 innings.
"I think Ricky's got better stuff than what he's shown us. That's my opinion," said Marlins manager Ozzie Guillen. "This is the first time I've seen this kid pitching consistently. I think sometimes he just goes through the motions. That's what I've seen. Ricky should be doing better than what he has."
Marlins: LeBlanc replaces Zambrano in rotation
Carlos Zambrano has been moved to the Marlins' bullpen, and lefty Wade LeBlanc will assume his spot in the rotation.
Zambrano, acquired from the Cubs in an offseason trade, has struggled in his first year with the Marlins. He is 1-8 with a 7.62 ERA since June 9 and has issued 67 walks in 115 innings. LeBlanc has been reliable in a long relief role, with a 1-1 record and 1.15 ERA in 11 games.
Guillen said there is still a chance that Zambrano could start Game 2 of Friday's doubleheader in Washington. That decision will be made depending on Zambrano's performance during Miami's four-game series against Atlanta. He threw 1 2/3 innings of relief on Monday, allowing one unearned run on two hits.
Jose Reyes extended his hitting streak to 17 games with a two-out double in the third inning on Monday. His streak is the longest active streak in the Majors and three games shy of his career high, set from July 17 to Aug. 7, 2005.
Braves: Kimbrel joins exclusive club
Craig Kimbrel earned his 30th save of the season in Atlanta's 2-1 over Philadelphia on Saturday. With the save, Kimbrel joined Mark Wohlers and John Smoltz as the only Braves with at least 30 saves in back-to-back seasons.
Kimbrel led the National League in saves in 2011, with 46. The 24-year-old is in his second full season and has a 1.35 ERA and a 0.65 WHIP in 40 games.
"It means our team is playing a lot of close games -- we're in a lot close games and we're winning a lot of ballgames," Kimbrel said. "If we didn't play winning baseball, I wouldn't have those opportunities."
Chipper Jones is batting .364 with eight doubles, four homers and 15 RBIs in 21 July games. He has raised his batting average, from .292 to .316, over that span.
The Braves have the season edge over the Marlins, 7-2.
Braves catcher Brian McCann has homered six times off Nolasco in his career, and has a .346 average in 52 at-bats against him.