Pettitte strained the flexor tendon in his left elbow during the Astros' game against the Cardinals, and Everett was scratched at the last minute with a strained right groin. Both are listed as day-to-day.
Brad Ausmus knew that something was wrong when Pettitte's fastball to Preston Wilson in the third inning clocked in at a much slower speed than his previous pitches.
Pettitte sensed it, too, and his suspicions were confirmed when he checked the scoreboard that gives the speed of the pitch.
"I turned around and looked to see what my veloicty was, and it was 83 [mph]," Pettitte said. "I went down from 90 to 83."
Pettitte then threw a cutter to Wilson, who knocked the pitch to left field for a two-run homer. It was at that time that Pettitte told Ausmus that his arm was hurting.
"The first fastball he threw to Preston, I could tell right away because of the velocity that something was bothering him," Ausmus said. "I wasn't sure if it was his arm or something else."
Moments later, Pettitte exited the game with an injury that has pretty much remained on the back burner ever since he returned to the mound after having major surgery to repair a tear in his elbow two years ago.
Perhaps trying to overcompensate for a sore left ankle, Pettitte suspects that a change in his mechanics may have sparked his latest arm ailment.
"That's really the only thing I can think of that might have given me some trouble tonight," he said. "I felt good starting the game out. When [Scott] Rolen got jammed and hit the ground ball to second, I kind of jarred my ankle a little bit. It started bothering me a little bit, but I didn't feel like I was really doing anything that much.
"My arm hasn't been giving me problems all year. That's the only thing I could think that maybe caused me to have a little flare-up with it."
"It's his pushoff leg," Ausmus said. "If there's pain involved when he pushes off, he's going to end up just falling foward and using more of his arm to compensate for lack of leg drive."
Pettitte sounded hopeful that he would be able to pitch in five days, but he wasn't making any guarantees. He understands why alarm bells start ringing as soon as the nature of his injury was revealed, given his elbow history.
"Since I've been throwing so good this year, obviously, it's alarming," he said. "But it's what I've dealt with ever since I've been here. Really, it's whatever I can pitch with. As long as I feel halfway decent, I feel like I can go out there and do something."
Pettitte wanted to reserve judgment on his immediate future until he can gauge his condition after a few days of rest.
"In my mind, I feel like I have a chance," Pettitte said of the possibility of making his next start. "I really don't know. I have to see how I feel tomorrow. I've felt absolutely terrible the day after I pitched before and felt like there was no chance I was going to make a start, and I was able to. I just really have to see how I feel after the next couple of days."
Everett's injury popped up in the seventh inning of Monday's game, while he was fielding a Yadier Molina ground ball.
"It got me pretty good," he said. "I iced it last night, thinking it would hopefully go away. It really didn't."
The injury is in the right hip flexor/groin area. Everett was scratched from the lineup minutes before game time once he tested it during batting practice, hoping for better news.
"I tested it during batting practice to see how it was going and decided if something bad were to happen, they'd lose me for the rest of the season," Everett said.
Alyson Footer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.