Mark McGwire, the former single-season home run king, announced his retirement Sunday after two injury-plagued seasons.
McGwire strongly hinted of retiring several times this year, when he batted .187 with 29 home runs for the Cardinals as he was slowed by an injured right knee.
McGwire agreed to a $30-million, two-year contract extension in spring training but never signed the deal.
"After considerable discussion with those closest to me, I have decided not to sign the extension as I am unable to perform at a level equal to the salary the organization would be paying me," McGwire said in a statement that was first released to ESPN.
"I believe I owe it to the Cardinals and the fans of St. Louis to step aside so a talented free agent can be brought in as the final piece of what I expect can be a world championship-caliber team."
The timing of the announcement took the Cardinals by surprise.
Manager Tony La Russa said he and McGwire have spoken often since the end of the season, and the slugger hadn't told him about the decision.
"I would believe he would have told the Cardinals first," La Russa said.
"The guy is a first-class guy. I find it hard to believe he wouldn't call the owners or (general manager Walt) Jocketty first."
By announcing his retirement before the free-agent season begins instead of closer to opening day, McGwire allows the Cardinals to pursue a replacement.
Jason Giambi, McGwire's protege from Oakland, is the top slugger on the market and likely will be targeted by the Cardinals as the replacement at first base.
McGwire captured the nation's attention in 1998 while hitting 70 homers to break Roger Maris' 37-year-old record. It was a short-lived mark as Barry Bonds hit 73 homers this season.
McGwire has 583 home runs, fifth on the career list, and finished his career 17 shy of becoming the fourth player to hit 600 homers.
McGwire, who began his career with Oakland in 1986, won the World Series with the A's in 1989 and reached the postseason six times. He was traded to St. Louis midway through the 1997 season.
"For years, I have said my motivation for playing wasn't for fame and fortune, but rather the love of competing," McGwire said in the statement. "Baseball is a team sport, and I have been lucky enough to contribute to the success of some great teams."
McGwire labored through the 2000 season with a bad right knee, missing virtually all of the second half.
He had surgery to correct patella tendinitis but again struggled with the knee this season.
HOME RUN LEADERS
1. Hank Aaron 755
2. Babe Ruth 714
3. Willie Mays 660
4. Frank Robinson 586
5. Mark McGwire 583
7. Barry Bonds+ 567
8. Reggie Jackson 563
9. Mike Schmidt 548
10. Mickey Mantle 536