Lee writhed on the ground in pain for several minutes before being helped off the field on a cart. A preliminary chest X-ray at the hospital showed no fractures, the team said. A CT scan confirmed a left rib contusion, and the Astros said Lee is day to day.
"I don't want to hurt anybody," shortstop Sanchez said. "I was trying to make a play, and he was trying to make a play, and it just happened. It's tough luck."
Lee was charging in for Mark Kotsay's pop fly and Sanchez was going away from the infield while tracking the ball. As they both slid, Sanchez's right knee struck Lee's midsection. Lee tried to throw the ball to the infield from the ground despite his obvious pain. Sanchez began signaling for a trainer.
"He looked like he was in pain," Sanchez said. "Any time you hit your ribs, it's really painful."
The injury came in the seventh, an inning after Lee, who'd entered the game in a 2-for-27 slump, socked a three-run homer to left field to give the Astros a four-run lead. Jason Bourgeois, who was playing center field, moved to left field, with Michael Bourn entering the game and taking over in center.
Lee, the Astros' cleanup hitter, is second on the team in RBIs, with 18, but has struggled at the plate. He went 2-for-3 on Sunday and is hitting .207.
"When he gets over this, he's going to come back and be fine," manager Brad Mills said. "He had the two hits and the big home run, which was nice, obviously. When he's healed, he'll pick up right where he left off. He'll be fine."
Bourgeois had a good look at the play from center field.
"That's two guys going hard after a ball," Bourgeois said. "Carlos is going hard, and he's a big man, and Sanchez is going hard as well. You just never know with those plays. Those are always scary."
Lee was involved in a similar play in 2007, when he collided in the outfield with Adam Everett and broke the shortstop's right leg. Lee also slid on that play, while Everett tried to make the catch standing up.
Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.