HOUSTON -- The Mets left Houston with even more questions on the pitching side. It’s the position that has been plagued most by the injury bug, especially their starting rotation. 

Carlos Carrasco has stepped in and played a pivotal role while aces Jacob deGrom and Max Scherzer are sidelined. Entering Wednesday, he had the second-most innings pitched on the team (75) with an 8-2 record and an ERA of 3.96.

But Carrasco left his start early with lower back tightness after allowing five runs on four hits in 2 1/3 innings pitched in the Mets’ 5-3 loss to the Astros. 

“I was trying to do my best and throw my pitches, but I couldn’t finish,” Carrasco said. “I couldn’t get to my pitches and everything was left in the zone. Every pitch they hit out, it was right in the middle because I couldn’t pitch.”

It is not the first time Carrasco has faced injury, as he has been placed on the IL a total of seven times in his career. It was looking different this year as he was making his 14th start of the season, something he has not done since the 2018 season.

The back tightness is a new challenge for the righty, but he was “not worried” about this injury as he headed to Miami to get an MRI on Thursday.

“I will be fine,” Carrasco said. “I felt it a little in the beginning. It got tighter with every inning, then I couldn’t finish my last two pitches. I couldn’t finish my delivery.”

If Carrasco has to miss time, he’ll be the fourth starter presently on the IL, along with deGrom, Scherzer and righty Tylor Megill. The Mets’ rotation injury problems started in Spring Training when deGrom was diagnosed with a stress reaction in his right shoulder. He faced live batters on June 21 in Port St. Lucie, Fla., but he still doesn’t have a timetable to return.

The Mets were covered with their big offseason acquisition in Scherzer, but he left with an oblique issue during his May 18 start against the Cardinals. That discomfort turned out to be a moderate to high-grade internal oblique strain, which has forced him to miss a month so far. He made a rehab start on June 21 and seems to be on track to make his return Sunday against the Marlins, according to Mets manager Buck Showalter.

Megill recently returned from a month on the IL due to biceps inflammation and found himself back on the IL with a right shoulder strain after exiting his June 16 start early. He was placed on the 15-day IL on June 17, and he’ll be re-evaluated in a few weeks.

That's without accounting for the bullpen, where three pitchers (Sean Reid-Foley, Joey Lucchesi and John Curtiss) recovering from Tommy John surgery have a slim chance of returning this season, along with shorter-term injuries to Trevor May and Colin Holderman, who both could return in July.

These injuries have forced players like Trevor Williams to step in. Williams has been a do-it-all pitcher, splitting his time between starting and relieving.

Tuesday’s outing, however, showed why he prefers the long man role of eating up innings during the middle of the game. Williams allowed three runs on four hits in his four-inning start.

Williams and the rest of the bullpen will need to play a pivotal role moving forward. They have been up to the task so far this season as they're fifth in the NL in bullpen ERA (3.68), tied for fourth for opponent's batting average (.225) and second in strikeouts per nine innings (10.23).

“This is a team where everyone is important,” Mets reliever Yoan López said in Spanish. “The injuries have not been on our side this year, but the bullpen is strong and ready. There are a lot of us in there that could go multiple innings, so we are ready and prepared. The injuries are tough, but there will be a time when we are fully healthy and pitching will be 100 percent.”