The Diamondbacks removed McCarthy from their NL Wild Card Series roster about 10 minutes before their Game 1 victory on Tuesday. Utilityman Jace Peterson replaced him on the roster.
"I was just visiting with him in right field as I do, I'm walking around during BP, I was out there joking around with him," Lovullo recalled Wednesday before Game 2. "I got a tap on the shoulder five minutes later saying he took his first couple of swings of BP and felt a pop. I went and saw him in the training room and he looked very uncomfortable."
Under MLB postseason rules, McCarthy wouldn't be able to play for the Diamondbacks until the NL Championship Series. McCarthy apparently would need at least that much time to recover.
"It's not going to be days," Lovullo said. "It's going to be weeks."
McCarthy, 26, batted .243 with a .318 on-base percentage, two homers, 16 RBI and 26 steals in 99 games this season.
Peterson, a member of the Brewers from 2020-22, batted .183 with a .276 on-base percentage, no homers, nine RBI and four steals in 41 games for the Diamondbacks after they acquired him from the Oakland Athletics at the trade deadline. The 33-year-old hit .221 with six homers, 28 RBI and 11 steals in 92 games with Oakland.