SAN FRANCISCO — The road to October just got a little longer for the Cincinnati Reds.

Middle infielder Matt McLain, the Rookie of the Year candidate who ignited the lineup since his debut in May, suffered a right oblique strain over the weekend in Arizona and went on the 10-day injured list Monday before the Reds’ series opener against the San Francisco Giants.

“Obliques I know first hand, it’s something you can’t mess around with,” manager David Bell said. “You you have it you can’t play with it. The severity of it can make a big difference. We’re really hoping it’s on the mild side and he can return quickly.”

One reason for that kind of optimism, Bell said, is that McLain has been able to play through discomfort before finally saying something to the staff after Sunday’s game in Arizona.

“He definitely did the right thing to let us know so we could now be on top of it,” Bell said.

McLain got an MRI Monday, and as of late Monday, doctors were still looking at the results to determine whether it was closer to a Grade 1 or Grade 2 strain.

McLain, 24, is hitting .290 with 16 home runs and leads the team in WAR.

He has started at shortstop and second base since his May 15 debut, most recently settling into the everyday second base role with Jonathan India (foot) on the IL.

McLain, who went 0-for-4 with three strikeouts Sunday, joins India, Joey Votto (shoulder) and lefty-hitting outfielder Jake Fraley (toe) among key Reds hitters now on the IL.

He said the side has been bothering him the last couple of series, increasingly feeling the pain on checked swings and misses.

“It just it got to the point where it hurt to do just about everything. I had to say something,” said McLain, who was hesitant to come out of the lineup given the importance of these games as the Reds chase a playoff berth.

“That’s the worst part, the position that we’re in,” he said. “But unfortunately that’s part of it. I’m going to do everything I can to get back as soon as I can. It sucks for sure.

“But this team’s more than capable without me. I’m not the team or anything,” he added. “We have the pieces. We have everything we need to go win games. But I do want to get back out  there and be with my teammates.”

The Reds activated outfielder Stuart Fairchild from the 7-day concussion list in a corresponding move Monday. Fairchild was in the lineup playing right field Monday.

Spencer Steer, who had become the everyday left fielder in recent weeks, took over Monday at second, his natural position, and is expected to see most of the time there until McLain or India returns.