Left-hander Antonio Bastardo was placed on the 15-day disabled list late Monday night because of a strained shoulder.
Bastardo left injured in the fourth inning of his last start and returned to Philadelphia, where he saw a doctor on Monday.
Pitching against Tampa Bay last Thursday, the rookie gave up six runs in the first two innings to waste a 4-0 lead. He was replaced by Chad Durbin after a one-out walk in the fourth.
Bastardo is 2-3 with a 6.75 ERA in five starts and has lost his past three outings.
The Phillies were off Monday and begin a three-game series in Atlanta on Tuesday. Right-hander Joe Blanton will start the opener, with left-hander Cole Hamels pitching on regular rest in Bastardo's spot Wednesday. No starter has been announced for Thursday's finale.
Lefty reliever Sergio Escalona was brought up from Triple-A Lehigh Valley to take Bastardo's spot on the roster.
General manager Ruben Amaro Jr. says the Phillies have been shopping for pitching help in recent weeks -- without much luck.
"We have interest in a lot of guys and we have talked to several teams about pitching across the board," Amaro told MLB.com Monday. "But a lot of it just depends on which pitching becomes available. And if they do become available, if we have the right fits for them."
Amaro said boosting the output of the rotation is key, though the Phillies could stand to improve their bullpen, too.
The Phillies' starters have an NL-worst 5.21 ERA and are averaging fewer than six innings per game. The bullpen ranks 11th in the NL with a 4.11 ERA.
"When you have this many teams in the race it's very thin," Amaro said. "It's always thin. Again, there were three teams who got pitching last year. Three teams out of 30. That's 10 percent.
"We can say, 'Pretty please can we have a pitcher?' but that doesn't mean one will become available."
Real make Valencia bid
Atlanta Braves interested in Boston Red Sox pitcher Brad Penny, according to sources
Philadelphia Phillies’ Brett Myers out indefinitely with injured hip
