"It's a small tear," Phillies general manager Ruben Amaro Jr. said. "Basically it's how long he can manage through it."
Pettibone has battled shoulder soreness since last summer. He received a cortisone injection in February, and that proved to be a temporary solution. He made two spot starts for the Phillies in April and could not match the effectiveness he displayed during his rookie season in 2013.
Amaro noted that many pitchers have thrown with labrum tears. Mets righthander Dillon Gee suffered a partially torn labrum in 2009 and never had it surgically fixed.
Pettibone will attempt to strengthen the muscles and tissue around the labrum. Some heal, Amaro said; others do not.
"It depends on the player and how big it is," Amaro said of the tear. "It's not a big one. It's pretty small. But it's uncomfortable for him."
Pettibone's health is an issue because the Phillies lack starting depth in the minors. Buchanan was left unprotected in the Rule 5 draft last winter and became one of the last players invited to major-league spring training. He impressed team officials with his poise and command in the spring.
The 25-year-old righty posted a 3.98 ERA in nine starts at triple-A Lehigh Valley.
"He hasn't been dominant," Amaro said. "But he's been consistent and he's winning."
For now, that is enough to make him the Phillies' fifth starter.
Jimmy Rollins was on base three more times Thursday. He scored in the eighth inning after reaching with a walk. His on-base percentage is .376. It was .318 in 2013.
"It's just impressive, what he's been doing," teammate Marlon Byrd said.
Only Troy Tulowitzki, who is on an otherworldly pace for Colorado, has posted a better OPS among shortstops. His OPS is 1.217; Rollins is at .831. Rollins needs 252 more plate appearances to trigger an $11 million option for 2015.
Rollins rapped his 2,218th hit, pushing him ahead of Richie Ashburn for second in club history.
Ben Revere started for the first time in five games. He batted eighth and singled to start the ninth. Tony Gwynn Jr. pinch-hit and bunted Revere to second. But Rollins and Wil Nieves struck out against Miami closer Steve Cishek to end the threat. . . . The Marlins are 19-6 at home, which is the best in the majors. It is their best 25-game start at home in franchise history.