An MRI on Thursday revealed inflammation in the elbow and a
strain in his flexor tendon, according to the Astros.
It remains to be seen exactly how long Pettitte will be out, Houston manager Jimy Williams said after the Astros' 6-1 loss to Milwaukee.
"Let's see medically what happens first," Williams said.
"Your whole priority is to get his arm well.
"We have to wait until we go home to find out more information.
Plus, you have to get the words from the man, how he feels."
Pettitte left Milwaukee before the end of the game and was not
available for comment afterward.
The move was made retroactive to Pettitte's last start.
The left-hander allowed six runs on 11 hits over 5 1-3 innings in the loss to the Giants. He walked two and struck out three.
Pettitte was scheduled to start Monday at St. Louis. Jared Fernandez, a right-handed knuckleballer, will replace him, although Williams would not commit to keeping him in the rotation beyond that.
Pettitte was injured when he checked his swing while batting Tuesday against the Giants. An MRI, performed Thursday, revealed inflammation in his left elbow and a strain in his flexor tendon.
Making his Astros debut Tuesday, Pettitte allowed six runs on 11 hits over 5 1/3 innings. He signed to a three-year, $31.5-million free-agent contract in December after spending nine years with the Yankees. The Deer Park, Texas, native was 21-8 with a 4.02 ERA in 33 starts last season in New York.
"Start, relief, close, as a knuckleballer I'm there to do
anything," said Fernandez, who started six games for Houston last year. "Hopefully, Andy gets healthy quick. We definitely need him."
Pettitte went 21-8 with a 4.02 ERA in 33 starts last season in New York. His last stint on the disabled list came from April 21 to June 14, 2002, when he was out with left elbow tendinitis.
"Hopefully it's not that tough a blow," Houston's Jeff Bagwell said. "Hopefully, he does a little time there on the DL and is able to come back throwing well."
Pettitte, 31, with a 149-79 career record, has been a durable pitcher. He started a career-low 22 games in 2002.
The Astros added ex-Yankees Pettitte and Roger Clemens to their rotation during the offseason. Clemens' Houston debut went much better than Pettitte's: He beat Barry Bonds and the Giants on Wednesday.
Houston recalled right-handed reliever Brandon Backe from
Triple-A New Orleans to fill Pettitte's roster spot.
Information from The Associated Press was used in this report.