Manager Terry Francona's club, meanwhile, has more than held its own without him.
Choo faces his former team for the first time as these Ohio rivals open a unique four-game set Monday at Great American Ball Park.
After spending the previous six-plus seasons with Cleveland (27-22), Choo was sent to Cincinnati (31-19) as part of a three-team trade in December. The South Korea native, who can become a free agent after this season, is hitting .285 with a team-leading nine homers and 37 runs scored from the leadoff spot. He is, however, just 1 for his last 21.
"I think he's fit in real well," general manager Walt Jocketty told the team's official website. "He's really become a great teammate that I think is well admired by his teammates. He's been just a big plus to our club. He is the lift we were looking for, offensively."
Despite losing Choo, Cleveland ranks near the top of the majors in almost every offensive category, including runs (248) homers (64) and slugging percentage (.452). The second-place Indians sit 1 1/2 games behind AL Central-leading Detroit.
"I hope they play good all year," Choo said. "The last three or four years, they'd play good the first half and the start of the second go down. But I think they're a better team this year. ... Hopefully they keep playing well."
Contrary to Choo's remarks, Cleveland is mired in a 1-5 slump after dropping three straight at Boston. The Indians appeared headed for a victory Sunday before giving up four runs in the ninth inning of a 6-5 walkoff loss.
Things aren't about to get any easier against the Reds, who have taken four straight and 12 of 16 in the series at home. These clubs play again Tuesday in Cincinnati before shifting the series to Cleveland for two games.
"It's just two good teams playing against each other who happen to be in the same state," Indians pitcher Justin Masterson said. "I think the National League-American League thing, it's not (big) for the players. It's not as big and as crazy as what some would think."
Cincinnati had won five straight and 12 of 14 before suffering a 5-4, 10-inning loss to the Chicago Cubs on Sunday.
"This one got away," manager Dusty Baker said. "We'll start a new streak tomorrow. We've been playing good ball."
The Reds, who haven't dropped back-to-back games since April 30-May 1, will try to bounce back behind Mike Leake (4-2, 3.25 ERA). After allowing nine hits over 6 2-3 innings during a 4-0 victory at Miami on May 15, Leake threw seven innings of three-hit ball in Tuesday's 4-0 road win over the New York Mets.
"The guy has worked hard," Baker said. "He's throwing the ball as well as anybody we have."
The Indians counter with Ubaldo Jimenez (3-3, 6.04), who had gone 3-0 with a 1.90 ERA in his previous four starts before allowing six runs over four innings Wednesday in an 11-7 loss to Detroit.
Jimenez is 3-0 with a 3.09 ERA over five matchups against the Reds, but he hasn't faced them since 2010. Brandon Phillips is 2 for 13 in their matchups.
Jimenez, though, will need to be wary of Joey Votto, who's 5 for 12 against him. Votto is hitting .463 with four homers, 17 runs and 10 RBIs over his last 14 games.
Cleveland's Drew Stubbs, acquired in the Choo trade, is 3 for his last 23.
The Indians placed closer Chris Perez on the 15-day disabled list Monday with right shoulder soreness, one day after he left their game at Boston in the ninth inning. This is his first trip to the DL in more than four seasons.