Team spokesman Nick Piburn said an MRI taken Thursday night revealed a right rib fracture. Tulowitzki was injured earlier in the day while diving for a ball in the eighth inning of a 5-4 loss to the Washington Nationals.
"I'm not going to sugarcoat it. It's a big loss for us," Rockies manager Walt Weiss said Friday before Colorado hosted the Philadelphia Phillies.
"It's also an opportunity for our team to step up and do what I think we've done well all season and that's respond to adversity," Weiss said. "We're not going to make up that type of production regardless of who plays but there's no doubt in my mind we can still win games and be a factor in this race throughout the season."
Tulowitzki told the Denver Post in a text that he was in a lot of pain and was upset after working so hard to come back from an injury-plagued 2012 season.
He underwent season-ending groin surgery last June, and the Rockies stumbled through a franchise-worst 98-loss campaign.
Colorado has been much more competitive this year, and a big reason is Tulowitzki, who ranks second in the NL with a .347 batting average, third in homers (16) and fourth in RBIs (51).
"It's tough on him," Weiss said. "He worked really hard this offseason. He worked really hard every day to prepare himself to play. So there's a lot of frustration that goes along with that.
"It's going to be tough for him in the short term. I told him just make sure to keep your mind right because we're going to need you to lead us to a pennant, so get ready to do that."
Tulowitzki was the most seriously injured among three Rockies starters who left Thursday's game.
Carlos Gonzalez exited with a bruised left foot when he was struck while in the on-deck circle by a foul ball hit by teammate Jordan Pacheco in the first inning. Center fielder Dexter Fowler was hit on the right hand by a pitch from Ross Detwiler when he squared to bunt in the third.
Weiss said Gonzalez told him he was healthy enough to play Friday.
"He's not going to be 100 percent but he said he was good enough to play," Weiss said. "Putting his name in the lineup is huge for our club."
Fowler wasn't in the starting lineup but could be available if needed.
"Hand injuries are tough in this game, but he's definitely getting better," Weiss said. "Hopefully he'll be available in some capacity."
At least initially, Weiss said he expects to take a shortstop-by-committee approach in Tulowitzki's absence. Utility man Jonathan Herrera got the start Friday with Rutledge, who played shortstop for the Rockies when Tulowitzki was injured last season, getting the nod at second.
DJ LeMahieu, who can also play second and short, also figures prominently in the mix.
"I think all three of them are capable of playing shortstop, but I'll have to figure that out on the fly here," Weiss said. "Maybe there's matchups, maybe you play the schedule, and maybe a guy takes off. I'm not going to get locked into anything right now, but I think we've got three guys that can play the position."
Outfielder Michael Cuddyer, who returned earlier this week after missing five games because of a rib cage strain, is moving up a notch in the batting order to hit cleanup in place of Tulowitzki. Cuddyer was batting .337 with 10 home runs going into the series opener against the Phillies.
"For the most part, he's been a very productive player," Weiss said. "He's a tough out, drives in tough runs. He'll be fine in the cleanup spot."