Right-hander Michael Fulmer was shut down by the Detroit Tigers for an indefinite period of time Thursday, one day before his next scheduled spring outing.
"He took a step back to refine his lower-body mechanics," manager Ron Gardenhire said, reading from a statement written on a legal pad, after the Tigers and Red Sox played to a 4-4 tie. "We have no timetable on when he's going to get back on the mound."
Asked follow-up questions by a reporter, Gardenhire said, "We're not going to go any further than that. We have to let him do his thing and let the trainers do their thing."
Fulmer, the 2016 American League Rookie of the Year, was not available for comment.
Knee problems cut short his 2018 season in mid-September, as he finished 3-12 with a 4.69 ERA in 24 starts over 132 1/3 innings. He was expected to make a full recovery from a September surgery, the second on his right knee.
In his most recent spring start March 9, Fulmer threw 44 pitches over three innings, allowing four hits and two runs against the Atlanta Braves, who beat the Tigers 6-4. His highest pitch velocity was 92 mph.
"It's not like it just vanished," Fulmer said after the outing, according to the Detroit News. "It's going to come back. My command today was the best it's been this spring. The sinker was moving all over the place. I got a couple of punch outs with it ... the changeup, too."
In his first season with the Tigers in 2016, Fulmer went 11-7 with a 3.06 ERA and 132 strikeouts in 159 innings.