An X-ray taken Friday revealed the fracture.
"It will be every bit of six weeks, would be my guess," Rockies manager Jim Tracy said. "I'm not going to shy away from the fact that this is quite the punch in the gut. ... To sit here and try to tell you it's a real box of chocolates, shame on me."
Regular second baseman Clint Barmes likely will move to shortstop. Tulowitzki's roster spot was filled by former first-round Draft pick Chris Nelson, who was recalled from Triple-A Colorado on Friday.
"The report I got was that he's still somewhat of a work in progress defensively at second base," Tracy said of Nelson. "He's done a fairly credible job at shortstop. ... The word I got was from a comfort standpoint defensively, he's at a better place at shortstop than he is at second base."
It is just the latest bit of adversity facing Colorado (34-32) as the Rockies attempt to make a push in the National League West standings with six straight home games in the next seven days, beginning with Friday's series opener against the Brewers.
"It's unfortunate for us," Barmes said. "Obviously, I've been over there before and it's nothing new but we're losing a huge part of this team with what he brings offensively and defensively. There's nobody that can replace that on this team."
Tulowitzki, who has hit in both the No. 3 and cleanup positions in the lineup for the Rockies this year, leads the team with a .306 batting average and is second with nine home runs and 34 RBIs. Tulowitzki ranks in the top five among National League shortstops in average (second), slugging percentage (third) on-base percentage (first), home runs (tied for third) and RBIs (fourth).
Tracy said an MRI revealed there was no disjointed bone in Tulowitzki's bone, which would require season-ending surgery.
"That's the good news part of it," Tracy said. "There is a chip fracture and with time it will heal and will re-adhere itself to the bone and just be a piece that will heal back."
Nelson, the No. 9 overall pick in 2004, was batting .311 with five home runs and 20 RBIs for Colorado Springs this season.
"I'm just looking, whenever Tracy calls my name, to be ready," Nelson said. "Whatever opportunity I have to help the team, I'm going to make the most of it."
Joey Nowak is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.