Tulowitzki was hurt when he was hit by a pitch from Twins reliever Alex Burnett in the eighth inning of a win Thursday in Minnesota.
While the initial examination didn't reveal a break, an MRI on Friday found an avulsion fracture, where a fragment of bone tears away.
Tulowitzki was placed on the 15-day disabled list Friday afternoon and the Rockies recalled infielder Chris Nelson from Triple-A Colorado Springs to fill his roster spot.
It was a big blow for the Rockies, who have been hovering around .500 even as Tulowitzki helped buoy a struggling offense.
"I'm not going to shy away from the fact that this is quite a punch in the gut," Rockies manager Jim Tracy said before the game against the Milwaukee Brewers. "This is a very, very difficult player to replace, because of who he is, what he brings to the table each and every day."
Tracy said the team caught a break because Tulowitzki won't need surgery to stabilize the fracture. That would've placed him out for the rest of the season.
"We dodged that bullet. But we did not dodge the fracture part of it," Tracy said. "To sit here and try to tell you it's a real box of chocolates, shame on me."
The Rockies could soon have ailing outfielder Carlos Gonzalez back after he jammed his left knee while fielding a single the day before in Minnesota. Gonzalez has been another offensive bright spot, hitting .295 with a team-leading 10 homers.
"We're much closer on him, as far as getting him back on the field than maybe we initially anticipated," Tracy said, indicating that Gonzalez could be back in some capacity as soon as Saturday.
Having hit in the cleanup spot most of the season, Tulowitzki is batting .306 with nine homers and 34 RBIs.
He's also been a steady presence in the field, leading all major league shortstops in total chances (330), assists (201), putouts (124) and double plays (55).
"Tough blow," Rockies general manager Dan O'Dowd said. "He's one of the better players in the game. But they're going to keep playing the games, so we're going to have to figure out a way to move on."
This will be Tulowitzki's third stint on the disabled list and first since his injury-marred 2008 season. That year he tore his left quadriceps in May while making an awkward throw. Two months later, Tulowitzki sliced his right palm after slamming his maple bat into the ground in anger following his removal from a game.
"It's a huge hit to us," said Barmes, who came up through the Rockies system as a shortstop. "We're going to be missing a lot, having [Tulowitzki] out of the lineup -- offensively and defensively. It's not going to be an easy thing to do, but I believe in the talent on this team. I still believe we can score some runs and stay in it so when he comes back, there's still a chance toward the end to win the division and go back to the playoffs."
Nelson hit .311 with five homers for Colorado Springs and was in uniform for the game Friday. He's primarily played shortstop in his minor league career but has also seen some action at second and third.
"You don't expect Chris Nelson to come up here and be Troy Tulowitzki," Tracy said. "Every team in baseball has specific players and/or a player on their club that if you are to sustain an injury that is going to cover a period of time, it's going to take the effort of all to get through it. [You can't] expect one guy to now pick up the load and carry it by himself. It won't happen that way. It has no chance of happening that way."