"I'm crushed," Ellis said. "You play the whole season to get to this point and now I can't play because of this. ... I'll be the best cheerleader we have."
The injury is a costly one for the A's, who lead Minnesota 2-0 in the division series but must try to close it out without their top three middle infielders.
Shortstop Bobby Crosby, the 2004 AL Rookie of the Year, is sidelined with a back injury, and backup Antonio Perez underwent surgery Thursday on his broken finger. D'Angelo Jimenez will start in Ellis' place Friday in Game 3.
Manager Ken Macha said injuries are part of the game but acknowledged Ellis will be missed for both his bat and glove.
He's "one of the top defenders in the American League at second base," Macha said Thursday. "You know when balls are hit there, the guy's out. He gets the big hit every once in a while."
Ellis made only two errors in 632 regular-season chances, breaking Bret Boone's record for best fielding percentage by a second baseman. Ellis' .99684 percentage narrowly edged the mark of .99671 set by Boone for Cincinnati in 1997.
Ellis went 2-for-4 with two singles in Game 2, injuring himself in the ninth inning swinging at a pitch from Joe Nathan. Ellis waved his hand and appeared to be in pain while trainers looked him over.
He finished the at-bat by striking out looking and was replaced by Jimenez at second base in the bottom of the ninth.
The bone was broken in three places and will take three to six weeks to heal. Trainer Larry Davis said Ellis would be unable even to pinch-run the rest of this series.
The A's can replace Ellis on the roster if they advance to the next round, with Mark Kiger and Kevin Melillo the most likely options.
Jimenez, picked up by Oakland in June after being released by Texas, played in just eight games for the A's, going 1-for-14. He batted .183 for the season with one homer and eight RBI in 71 at-bats and made four errors in 18 games at second base.
He has played parts of seven seasons in the majors, with his best season coming in 2004 when he hit .270 with 12 homers and 67 RBI for Cincinnati.
"It's not like I've never been there before," Jimenez said. "It will be the same game. I will just go out there and do my best."
Ellis batted .249 with 11 homers and 52 RBI this season but finished strong. He hit .308 with six homers and 26 RBI in his final 49 games.
Oakland has dealt with numerous injuries this season, overcoming DL stints by Frank Thomas, Milton Bradley, Rich Harden, Huston Street, Esteban Loaiza, Joe Kennedy, Ellis and Crosby to win the AL West.
"That's the good thing about this team: We're a good bench," said shortstop Marco Scutaro, who has filled in well for Crosby. "People get hurt and there's always the bench. No matter who's playing second, I have to throw the ball and make double plays. Communication will probably be good. He speaks Spanish and I do, too. D'Angelo's been in this game for a long time. I don't think it's going to be different."
Crosby missed the final 52 games of the regular season with a back injury. He said Thursday that he's not getting any better and doubts he'd be able to play if the A's advance past the first round.
"He has not done any baseball activity," Macha said. "It'll be very difficult for him to get back and play."