PHOENIX -- The D-backs lost to the Giants, 11-4, on Friday night at Chase Field, but of bigger concern was Zac Gallen being forced to leave his start during the third inning.

The initial diagnosis was right hamstring tightness, but Gallen will have an MRI exam on Saturday to try to determine whether there is a strain.

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Losing Gallen would be tough news for both the D-backs, who are already without a trio of starting pitchers, and Gallen, who has had two stints on the injured list already this year.

"We're going to keep our fingers crossed for the best possible news," D-backs manager Torey Lovullo said.

Gallen was not sharp from the beginning of the game, as he allowed a pair of runs in the second inning and a leadoff homer in the third.

Following that homer by Alex Dickerson, Gallen allowed a single to Brandon Crawford. Then Gallen collapsed on his follow-through on a 1-2 pitch to Wilmer Flores.

The D-backs’ dugout did not immediately react because they were focused on the pitch to the plate and not Gallen.

"We're not necessarily watching what Zac’s doing, and we just saw him on the ground and obviously worried that he didn't get up and didn't look very comfortable," Lovullo said. "So I originally thought it was an ankle or a twisted ankle."

Once he learned that it was a hamstring and not an ankle, Lovullo made the decision to remove Gallen from the game.

Gallen told Lovullo that he felt the hamstring on the previous pitch, but that it really grabbed him on the 1-2 pitch and he knew it was a problem. Even the fierce competitor that he is, Gallen understood he needed to come out of the game.

"You know Zac, every time I do take him out of the game, it's like it's getting ready to be a fistfight between he and I," Lovullo said. "And I enjoy those interactions. But I could sense, I've seen enough of his expressions, and I know what he looks like when he's a little bit disappointed and I could quickly tell that there was going to be limited pushback."

The team's telecast showed Lovullo crouching in front of Gallen, who was seated on the bench after being removed, and talking to his right-hander.

It's been a frustrating season for Gallen, who was outstanding for the D-backs in 2019 after coming over in a Trade Deadline deal and then again last year.

Gallen suffered a fracture in his right forearm this spring while taking batting practice, and he opened the season on the injured list.

Then after he recovered from that, he sprained his right elbow and was out from May 7-June 17. Now, if there is something wrong with the hamstring, he could be looking at a third stint on the IL.

"It's happened a couple times with him already, and I feel terrible for Zac," Lovullo said. “He is grinding away at trying to maintain good health and just when he gets his feet under him, you know, things start sliding backwards, and it's for little things that really are not his fault."