Tyler Fitzgerald of the SF Giants leaves the game against the Brewers in the third inning

SAN FRANCISCO – When the Giants took the field to start the third inning against the Brewers on Thursday night, it was Brett Wisely and Marco Luciano who filled the two middle infield positions.

Tyler Fitzgerald, who started the game at shortstop, was taken off the field due to tightness in his lower back, the club later announced. He will undergo an MRI scan Friday morning. Although the injury was severe enough to force him to leave the game, Fitzgerald said he is not too concerned about the long-term prognosis.

“It's nothing I'm too worried about; it's just worked out pretty well,” Fitzgerald said after the Giants' 3-0 loss. “I felt it in the warm-up before the game and tried to keep playing anyway.”

As he ran to first base on his lineout into right field in the first inning, Fitzgerald said, “I just knew something was wrong.” He entered the field for the start of the second inning and ended the inning with a two by catching a sharp ground ball from Sal Frelick, stepping to second base and throwing to first base. At that point, he said, “I just thought it wasn't worth it.”

“It’s completely sealed off at the moment, so probably a smart decision.”

Interestingly, Luciano took over second base while Wisely slid into Fitzgerald's spot at shortstop.

Fitzgerald, 26, has already made a strong impression, and he will be a central part of the Giants' plans next spring. Fitzgerald, who earned the starting shortstop spot midseason, has a .296 batting average, 14 home runs and 17 stolen bases, the most on the team, in his first full-time major league appearance.

It was more difficult for Luciano. He seemed destined for the job at the end of last season, but was knocked out by Nick Ahmed in the spring and spent the season alternating between San Francisco and Triple-A Sacramento, spending less and less time at shortstop.