Mark McGwire injured his surgically repaired right knee and was out of the St. Louis Cardinals' lineup for Friday's doubleheader against the Florida Marlins.
Manager Tony La Russa said McGwire "tweaked" his knee on a cutoff play Thursday night. McGwire aggravated the injury taking a pitch later in the game and his knee buckled a bit when he took a called third strike for the final out in a 2-1 loss to the Atlanta Braves.
"I think it's smarter to be concerned," La Russa said. "Yeah, I'm concerned. He's worked hard to get back into the lineup, so to miss a game it's got to be something you pay attention to."
McGwire underwent therapy on his knee earlier Friday and was waiting to see team doctors.
McGwire was batting .198 with 19 home runs and 39 runs batted in. He has 573 career homers, tied with Harmon Killebrew for fifth place.
The Toronto Blue Jays released right-hander Joey Hamilton and sent third baseman Luis Lopez to triple-A Syracuse.
Hamilton, in the final year of a three-year $16.5 million contract, was 5-8 with a 5.89 earned-run average.
He was heavily booed after his last start, Sunday in Toronto, when the New York Yankees scored eight earned runs on 10 hits in five innings.
The Kansas City Royals signed reliever Jason Grimsley to a two-year contract extension.
Grimsley has an 0-5 record but leads the team with a 3.00 ERA, ninth among American League relievers who have pitched at least 50 innings. He also is tied for fourth in the league with 50 appearances.
Left-handed pitcher Chris Seddon from Canyon Country Canyon High, the Tampa Bay Devil Rays' fifth-round draft choice, signed a contract with the club.
Seddon, who gave up a scholarship to Loyola Marymount, was assigned to Princeton, W. Va., the Devil Rays' rookie league team.
Florida put outfielder Eric Owens on the 15-day disabled list with a sprained right knee. The Marlins also activated right-hander Vladimir Nunez, who had been sidelined since July 19 with a pulled right quadriceps. . . . The Detroit Tigers recalled right-hander Luis Pineda from triple-A Toledo and left-hander Kevin Tolar was sent to Toledo. . . . The Cleveland Indians sent reliever Tim Drew to triple-A Buffalo.