SCOTTSDALE, Ariz. -- D-backs left-hander Eduardo Rodriguez, counted on to be the team’s No. 3 starter, was diagnosed with a lat strain and will open the season on the injured list, with the length of his absence still to be determined.

Rodriguez felt discomfort while warming up for the second inning Tuesday night against the Cubs. While the veteran said the lat is already feeling “95 percent,” results of an MRI taken Wednesday showed a strain.

“He's going to be shut down from throwing until he's asymptomatic,” D-backs manager Torey Lovullo said. “I know you guys want to know lengths of time, all the common questions that I want to know, but we don't know. That's gonna depend on how he progresses and how he's feeling day by day. We're going to assess it daily, and then build it up from there and the return will be determined by the length of time that he's down.”

Here are some things to know about the news and how it impacts the D-backs' roster decisions.

Rodriguez seems confident it won’t be long
Rodriguez said he was surprised by the results of the MRI, saying he thought it would not show a strain.

“I don't feel the way that it showed,” Rodriguez said. “I know this isn't gonna be too long. I just feel like it was a little tightness in there, but I feel great today. I know I’m going to be back faster than we think.”

The key will be how long he’s shut down from throwing
As a starting pitcher, Rodriguez will need to be built up to somewhere around 65-75 pitches before he will be considered ready. If he doesn’t throw for more than a week to two weeks, that would mean he would need to start over from scratch to build up his pitch count.

Rodriguez, though, remains optimistic that he won’t have to be inactive for that long.

“That's when you got to start from zero,” Rodriguez said. “And as a starting pitcher, starting from zero -- that means, like, you gotta go do live [batting practice sessions], bullpens, two innings, three innings until you go to 75 pitches. And that’s a long time, so I want to make sure I don’t have to go through all that.”

What does this mean for the rotation?
One of the reasons the D-backs signed Rodriguez to a four-year, $80 million deal this winter was to avoid having to have three young pitchers in the rotation.

At least for the start of the season, that’s exactly what they will have.

Zac Gallen and Merrill Kelly will head up the rotation, and Brandon Pfaadt will slide up from the No. 4 spot to take Rodriguez’s place.

That leaves two open rotation spots with three starters -- Tommy Henry, Bryce Jarvis and Ryne Nelson -- still in camp as candidates. Nelson and Henry were the frontrunners for the fifth spot, while Jarvis has had an impressive camp.

It would not be a surprise to see the D-backs keep both Nelson and Henry as starters and have Jarvis be a length option in the bullpen to start the year.

“We are going to be OK,” Lovullo said. “We're going to be fine because we have understudies, we have players in the position that are going to cover this until he steps back into the arena. That's what good teams are able to do.”

Speaking of length in the bullpen
The D-backs have been internally debating whether or not to carry a long reliever to open the season.

Now, with Rodriguez opening the year on the IL, it seems like they almost assuredly will.

“The equation has changed a little bit because we're going to have three young pitchers in our starting rotation,” Lovullo said. “So we have discussed what that could look like and we have discussed how we can counter that. Maybe there was a 10 percent chance that we would carry a long guy and that percentage has increased dramatically.”