LAKELAND, Fla. – Michael Fulmer's comeback from offseason knee surgery has been put on hold. The Tigers right-hander, who was on turn to start Friday, “took a step back to refine his lower body mechanics,” manager Ron Gardenhire said Thursday.

“We have no timetable when he’s going to get back on the mound,” Gardenhire continued.

Neither Gardenhire nor pitching coach Rick Anderson offered any other details beyond that statement.

 "We'll let him do his thing, and the trainers," Gardenhire said.

Fulmer underwent surgery last fall to repair a torn meniscus in his right knee. He has been pitching this spring with a brace on his knee, a move he said is meant to help refine his delivery.

Fulmer has given up seven runs on 11 hits over eight innings in three starts this spring, walking four and striking out six. His fastball, which has usually registered in the mid-90s, has sat at 89-92 mph on radar guns this spring, topping out at 93 mph in his second start.

After his last start last Saturday, Fulmer said he would be working on regaining explosiveness in his lower body to regain some of that velocity.

“The strength’s there. The pain’s gone. All we need to work on in is explosiveness,” Fulmer said last Saturday. “That’s something we haven’t really been focused on, because when you come back from surgery, you’re working on strengthening all those muscles. You’re not really working on those fast-twitch fibers quite yet, the explosiveness, because you don’t want to be cutting back and forth with a knee injury. That’s kind of our next phase.”

Fulmer was not available for comment Thursday.

With Fulmer out for now, Daniel Norris and Spencer Turnbull take on more importance in their quest to crack the Tigers' rotation. Norris threw three scoreless innings Tuesday against the Red Sox. Turnbull starts Friday in what would’ve been Fulmer’s slot.

Castellanos day-to-day with left hand soreness

Nicholas Castellanos, who hoped to return to the Tigers lineup on Thursday, remains out with soreness in his left hand, which was hit by a pitch last Sunday.

Though Gardenhire said earlier in the week he expected Castellanos back Thursday, Castellanos had lingering soreness when he took light batting practice in the indoor cages Thursday morning.

“It's getting better, but it's still sore,” Castellanos said. “Today was my first day swinging a bat.”

Castellanos will try hitting again Friday. He won’t play the afternoon game against the Rays, but is day-to-day after that.

Boyd impresses in outing

Matthew Boyd’s fastball registered 94 mph on the Joker Marchant Stadium radar gun during his fourth outing of the spring on Thursday. More importantly, he had a buckling breaking ball that had Red Sox hitters struggling to catch up.

“I think it’s a function of my mechanics,” said Boyd, who credited work with pitching coach Rick Anderson. “I really got back to the fastball at the midpoint last year, and I realized there was another gear. When I committed to my fastball, consequently everything else got better.”

Boyd allowed three runs on five hits over five innings with a walk and three strikeouts in the Tigers' 4-4 tie. He tossed three scoreless innings before giving up a two-run homer to Lakeland native Steve Pearce in the fourth, followed by a C.J. Chatman fifth-inning single scoring former Tigers prospect Gorkys Hernandez.

“The last few [innings], I started to miss up a little bit,” Boyd said. “But yeah, it was a good day.”

Quick hits

• Drew VerHagen, currently working back from inflammation around his right shoulder, has resumed playing catch. No timetable is available for his return.

• The sight of Tigers players holding their MLBPA meeting Thursday morning on one of the back fields, rather than in the clubhouse like most meetings, piqued interest. Castellanos said they moved it to freely discuss matters. The meeting lasted more than two hours.

“There was front office in the kitchen when we tried to have our meeting,” Castellanos said, “so we went out to Kaline [Field].”

Boyd called Thursday’s announcement from Major League Baseball that talks would begin early on the next Basic Agreement “a step in the right direction. The fact that there’s dialogue, that’s a step in the right direction.”

Up next

Turnbull takes the mound in his quest to crack Detroit's rotation as the Tigers visit the Rays for a 1:05 p.m. ET game at Charlotte Sports Park. Nicholas Castellanos is expected to be in the lineup as he returns from a bruised left hand.