CINCINNATI (AP) -- The Reds have lost top starter Johnny Cueto for at least a few weeks because of a strained muscle in his back, the third significant injury for the defending NL Central champions in the season's opening weeks.
Cueto went on the 15-day disabled list on Monday. The Reds called up right-handed reliever Justin Freeman from Triple-A Louisville, a boost to their often-used bullpen.
The Reds are likely to call up left-hander Tony Cingrani to start in Cueto's spot on Thursday.
Last year, the Reds made it through the regular season without one of their starters getting hurt. That streak ended when Cueto pulled an oblique muscle in the first inning of a playoff game against San Francisco, leaving their rotation in flux for the rest of a five-game series that the Giants won.
Cueto strained a back muscle during the fifth inning of a 3-1 loss in Pittsburgh on Saturday, forcing manager Dusty Baker to go deep into his bullpen. The injury was initially thought to be in his triceps, but an examination found the problem in the right side of his back.
It's unclear how long the Reds might be without their opening day starter and 19-game winner from last season.
"Hopefully only three, maybe four starts," Baker said. "Once he does come back, he has to get his endurance up, so we're really not putting a timetable on it. We're going to miss him, but we've got to carry on."
The Reds won 97 games last season - second-most in the NL - despite having the back end of their bullpen wiped out by injuries during spring training. They also lost Joey Votto for 48 games at midseason because of torn knee cartilage.
The injuries are piling up quickly for Cincinnati.
Left-handed set-up reliever Sean Marshall developed a sore shoulder late in spring training and went on the disabled list. Cleanup hitter Ryan Ludwick tore cartilage in his right shoulder while sliding into third base during the season opener and will miss at least the first half of the season.
Now, Cueto is gone.
"This is our ace," Baker said. "We already lost a couple of key guys in Marshall and Ludwick, so I hope we don't lose any more."
The Reds transferred Ludwick to the 60-day disabled list on Monday to make room for Freeman on the 40-man roster. The 26-year-old reliever will make his major league debut the first time he gets into a game.
Cingrani was limited to two innings in his start on Sunday, keeping him fresh so he could fill in for Cueto on Thursday. The 23-year-old pitcher has fanned 26 in 14 1-3 innings for Louisville. He will make his debut as well.