"Unless you have a crystal ball or you're Mother Nature, you're prepared for whatever it takes," La Russa said before Sunday's 4-2 loss to the New York Mets. "It could be sooner, it could be later, it could be as long as late August. I don't know."
McGwire went on the disabled list July 6 with pain in his right knee and hasn't played since, missing the All-Star game.
St. Louis, which has lost four straight for the first time this season and six of eight, is 7-13 since McGwire went on the DL. Its NL Central lead, 10 games on July 5, was cut to four games with Cincinnati's 7-4 win at Montreal.
"It's definitely a little different," Jim Edmonds said. "We have to learn from it. They pitch everybody a little differently, the guy in front of him, the guy behind him, because they're worried about him.
"They don't want to walk the guy in front of him, then they don't want to walk him (because) then they've got to worry about the guy following him."
McGwire is hitting .303 with 30 homers and 69 RBIs, playing 70 games and missing 34.
"He's getting treatment every day," La Russa said. "He's a little better. But he's not going to join us in Montreal, which is the way I look at it, the next series."
With McGwire out, the Cardinals have made moves to fortify their pitching, acquiring right-hander Mike Timlin from Baltimore after Saturday's game for first baseman Chris Richard and right-hander Mark Nussbecak, and getting left-hander Jason Christiansen from Pittsburgh after Sunday's game for minor league infielder Jack Wilson.
"We've been trying to get Christiansen for a couple of years, and we were finally able to do it," Cardinals general manager Walt Jocketty said. "Obviously, we're in desperate need of a left-hander. He's a left-hander with quality stuff."
Timlin pitched a hitless eighth inning in his Cardinals' debut on Sunday, striking out two and walking one.
"Changing teams is something tough to deal with, but it's quite a pick me up to go from fourth place to first," Timlin said. "I was pretty nervous. You want to get off on the right foot. You want to throw strikes."
La Russa said Timlin will be used primarily to set up closer Dave Veres but also will close on occasion
"He's had experience. I would use him anytime after the seventh," La Russa said. "I wouldn't hesitate to use him as a closer."
That's fine with the Timlin. The 34-year-old was 2-3 with a 4.89 ERA in 37 games with Baltimore.
"I pitch in relief, you go from there," he said. "I've done both jobs. Whatever they want me to do."
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