BALTIMORE -- Orioles right-hander Jason Hammel will have an MRI on Thursday to determine the extent of damage in his sore right knee.
Hammel left Tuesday night's game against Tampa Bay in the fourth inning. He was making his second start since undergoing surgery on the same knee in July.
Hammel was originally slated to have the MRI on Wednesday, but said the exam was pushed back a day because of scheduling issues.
"Hopefully by (Thursday) afternoon we'll have an idea what we're dealing with," Orioles manager Buck Showalter said. "I don't think we'll really know anything until we get the MRI back."
Hammel knows this much: His knee hurts too much to allow him to walk comfortably up a flight of stairs, let alone face stiff competition in the middle of a pennant race.
"Basically, it won't allow me to pitch. That's the way I can put it," he said. "Getting on a mound right now and trying to throw a pitch, that wouldn't work."
Although there wasn't much swelling in the knee overnight, Hammel said, "That raises more questions for me, like, what's going on?"
Obtained in an offseason trade with Colorado, Hammel was 8-2 with a 2.61 ERA on June 22. He lost his next four starts, in part because the knee was becoming a problem, and he went on the disabled list after making an early exit from a game in Detroit on July 13.
Hammel returned to pitch effectively against the New York Yankees last Thursday, but after his shortened stint against the Rays, he said his knee felt like it did that night in Detroit.
"I'm frustrated," Hammel said Wednesday. "That's all I can really be right now until something positive shows up."
Hammel's injury comes after Orioles right fielder Nick Markakis broke his left thumb Saturday when he was hit by a pitch from CC Sabathia. Markakis had two pins placed in his thumb on Tuesday and was wearing a large cast in the clubhouse Wednesday.
"Three weeks until I get my pins out, and then we go from there," he said.
Baltimore would have to get deep into the postseason for Markakis to return to action this year.
"You know, it's a long shot for him to be able to make that physically," Showalter said. "But one of the thing we learned here is Nick is one of our quicker healers."