"Usually, you can tell in the first four to five days," Dugger said. "The thing I'm pretty optimistic about is he's stronger today than he was last night, so that's a positive. But he's still pretty weak and sore."
Rockies manager Jim Tracy said he believes the Rockies have caught the injury early enough that rest and proper rehab could head off a worse problem. Tulowitzki has a history of leg muscle issues. Last year, for example, Tulowitzki missed four games and almost had to sit out the All-Star Game because of a left quadriceps injury, and he regularly is playing through some kind of issue.
The injury caused a number of changes to the batting order and daily lineup, but Tracy said it's a small price to pay to have their two-time All-Star shortstop healthy. Tracy said he hopes to avoid what the Dodgers are going through with star outfielder Matt Kemp, who is on the disabled list for the second time this season because of a left hamstring injury.
"In a best-case scenario [with Tulowitzki], we're looking at five or six days, and I don't like that at all, especially because of the type of injury that we're dealing with," Tracy said. "A case in point, I was watching some highlights last night, and I saw Matt Kemp walk off for the second time in two weeks with the same [hamstring] injury.
"A complete tear of either a hamstring or a groin is pretty much two, 2 1/2 months, something like that. I don't want to visit that, and I don't want to see us in a position where Troy Tulowitzki has to go out and play baseball carefully. I don't ever see that working."
Tulowitzki hoped to come back after a day or two off, but he said after Wednesday's game he knew the DL was a possibility. He thought it was an accumulation of playing for so long with the injury and a particularly rough day Monday.
The Rockies played 19 innings while sweeping a day-night doubleheader from the Astros. At one point in the first game, Tulowitzki grimaced and was slow getting up after diving unsuccessfully for a grounder up the middle.
"The doubleheader was a lot of innings," Tulowitzki said. "My legs were coming into [Wednesday] a little sore. That played into it a little bit.
"I don't think it got healthy the whole year. I was kind of playing on it. For me, the doubleheader was what took it to the next level."
Tracy also mentioned that Tulowitzki ranged into medium right-center field for a fly ball during Wednesday's game.
"That may have helped the situation, for lack of a better term," Tracy said.
Tulowitkzi's injury means right fielder Michael Cuddyer will move from fifth to cleanup, behind sizzling left fielder Carlos Gonzalez, who hit three home runs Wednesday night. Cuddyer, batting .271 with six home runs and 32 RBIs, hit a grand slam in the first inning of Monday's game.
Tracy said he needs Cuddyer -- who was 10-for-27 with five doubles, two home runs and nine RBIs in his past nine games leading to Thursday -- to discourage opponents from avoiding Gonzalez.
"What we need from that spot is some consistency," Tracy said.
Cuddyer, in his first season with the Rockies after 11 with the Twins, said he doesn't mind the challenge.
"I hit everywhere in Minnesota, third, four, five, six," Cuddyer said. "I'm not going to do anything different, no new approaches. I am who I am. You can't be anybody else just because you're in a different part of the lineup."
Tracy moved Marco Scutaro, the No. 2 hitter, from second base to shortstop. But to avoid taxing Scutaro, 35, the Rockies also will use Nelson, who was drafted as a shortstop, and DJ LeMahieu, who has plenty of Minor League experience at short.
LeMahieu started at second base Thursday night.