DETROIT -- Part of a catcher’s role is to recognize the telltale sign that a pitcher is off, whether mechanics or health. The sign to Bobby Wilson that something was wrong with Tigers starter Spencer Turnbull on Thursday came from Comerica Park’s giant scoreboard beyond left field.

Turnbull’s 1-2 pitch to Rangers third baseman Logan Forsythe registered as an 87.5-mph slider on the scoreboard, but it was actually a fastball. Wilson brushed it off until he saw Turnbull’s final pitch of the second inning, a called third strike on Rougned Odor, was an 87-mph pitch that read the same.

“I didn’t see him doing any gestures that would say that he was banged up,” Wilson said. “But obviously you look at the board and he’s a guy who’s 94-95 [with the fastball], and you see an 87-mph slider on the fastball, and you say, ‘Hey, something’s not quite right.’”

The problem, according to the Tigers, is right shoulder fatigue. It’s not expected to be a major problem, but it could put another wrench into what is already an injury-depleted rotation for Detroit.

“We’ll just see wait and see how he comes in [Friday],” manager Ron Gardenhire said after Thursday’s 3-1 loss. “Once he comes in, then we’ll know exactly what we have to do here. But there is no structural damage. Everything looked great [on the MRI]. Now we just have to see.

“If it’s fatigue, we’ll give him a break here, if that’s what everybody tells us and the doctor decides. But we’ll just have to see.”

Turnbull overcame a leadoff walk to retire the Rangers in the first inning before Joey Gallo punished him for a hanging sinker with a 408-foot home run to right field leading off the second. Turnbull struck out Texas in order from there, but his velocity was dropping.

Once the inning ended, Wilson alerted Gardenhire and pitching coach Rick Anderson. Turnbull told them he didn’t feel any pain, but the Tigers weren’t taking any chances. Nick Ramirez replaced Turnbull for the third inning.

It’s a speed bump, no pun intended, in what has been an encouraging rookie season for Turnbull. He entered Thursday second among Major League rookies with 81 strikeouts, third with 87 2/3 innings, fifth with a 3.29 ERA and tied for seventh with a .252 batting average allowed. The former second-round Draft pick has been an impressive presence since slotting into the rotation following Michael Fulmer’s Tommy John surgery in Spring Training.

Fulmer is one of at least two Detroit starters out for the season. Matt Moore was lost in April to right knee surgery for a torn meniscus. Tyson Ross has been out since mid-May with right ulnar nerve neuritis, with no timetable for a return while he rehabs in Lakeland, Fla. Jordan Zimmermann just returned last week after missing about two months with right elbow inflammation.

With all the injuries, the Tigers have gotten by with a four-man rotation for more than a month, slotting in spot starters and even an opener or two when needed. Detroit has still had opportunities to give Turnbull an extra day of rest, including twice this month.

But with a fifth starter needed for Saturday against the Nationals, plus another extra starter for next week’s four-game, three-day series against the White Sox in Chicago, Turnbull's absence could leave the Tigers scrambling. As it is, Ramirez’s three innings Thursday likely rule him out for any role Saturday.

Gardenhire said Detroit will bring up a starter for Saturday, but didn’t announce who. Left-hander Ryan Carpenter, who has made seven starts for the Tigers, would be on turn to pitch Saturday, but he allowed 11 runs Monday for Triple-A Toledo. Gregory Soto, who has made five starts for Detroit, would be on short rest after tossing three innings Tuesday, but he has made three starts on three days’ rest already.

Drew VerHagen has a 2.38 ERA in seven starts for Toledo after the Tigers outrighted him on May 11, but he’d have to be placed back on the 40-man roster. So would Kyle Funkhouser, the prospect closest to joining Detroit’s rotation. He tossed six shutout innings for the Mud Hens on Wednesday, and he won’t be ready to pitch again until next week.

If Turnbull is out for any length of time, the Tigers could need a combination of those pitchers just to get to the All-Star break in 10 days.