WEST PALM BEACH, Fla. -- Houston ace Justin Verlander has a mild strain of a back muscle and said it would "probably take a miracle" for him to pitch in the Astros' opener at Oakland on March 26.

In an effort to remain positive, Verlander quickly added, "but I don't want to leave miracles off the table."

The reigning AL Cy Young Award winner was hurt on his second-to-last pitch in Sunday's exhibition game against the New York Mets. He had an MRI on Monday and was diagnosed with a strained latissimus dorsi muscle. There is not a timetable for his return.

"Talking with doctors and looking at the scans, it's definitely not worst-case scenario," Verlander said. "Best-case scenario would be nothing. It's just probably somewhere in the middle of that."

The 37-year-old right-hander's velocity was down from his previous start, and he was removed after two scoreless innings of a scheduled four-inning outing.

"Hardly noticed it, to be honest," Verlander said of the injury-inducing pitch. "It didn't quite feel right, just felt maybe I was a little off mechanically or something -- kind of one of those spring things. Then in between innings, it started to tighten up a bit."

Groin tightness slowed Verlander earlier in spring training. He said he did not know whether the two issues were related.

Verlander had a similar lat injury during spring training in 2015 and did not make his season debut until June 13. He finished 5-8 with a 3.38 ERA in 133⅓ innings for Detroit.

"Scans can say a lot of stuff and MRIs can say a lot of stuff, but one of the most important things is how you feel physically," Verlander said. "I'm trying to be very truthful with myself. I'm trying to recall also how I felt in '15. I definitely feel better this time than then."

A two-time Cy Young winner and the 2011 AL MVP, Verlander was 21-6 with a 2.58 ERA in 223 innings last year.

Verlander led the league in innings last season even with Houston managing his workload with extra days off and cutting his starts short when the Astros had big leads.

"The innings piled up because I pitched well," Verlander said. "I would rather continue to pitch well and have the innings pile up."

Zack Greinke likely will be the only one of last season's top three starters to open the season on the active roster. He allowed one run in four innings against Detroit on Monday.

No. 2 starter Gerrit Cole left as a free agent and signed with the New York Yankees. This year's projected No. 3 starter, Lance McCullers Jr., is recovering from Tommy John surgery in November 2018. Jose Urquidy, fourth on the depth chart, showed promise in seven regular-season starts and four postseason appearances last year.

Josh James, Framber Valdez and Austin Pruitt were all vying for the final rotation spot prior to Verlander's injury.

"You're ultimately trying to cover 1,400 innings as best as you possibly can," Houston general manager James Click said. "The five guys that you say are your starters on Opening Day, I don't know the last time a team went through the season with only five of them. We know we're going to have to be six, seven, eight guys deep."

Verlander went from +450 to +600 to win the AL Cy Young at Caesars Sportsbook off the news that he's unlikely to be ready for Opening Day.

ESPN's Ben Fawkes contributed to this report.