Sanchez, who underwent an MRI and other exams when he first felt the injury, said he'll visit a specialist to take another look.
"Probably Dr. [James] Andrews," he said, referring to the noted orthopedic surgeon.
Sanchez's agent, Gene Mato, confirmed Tuesday that the right-hander will visit Andrews, who performed surgery on Sanchez's shoulder in 2007, as a precaution.
It's the latest setback for a Tigers team that has had plenty of pitching issues all season. More important, though, it's a setback for a former American League ERA champion and veteran front-line starter who has battled minor shoulder injuries and surgery in the past.
Though the Tigers fell out of realistic postseason contention weeks ago, Sanchez wanted to come back and pitch, if anything for peace for mind going into the offseason. His rehab progressed slowly, but it picked up momentum the last week or two as he stretched out his arm and felt stronger.
Sanchez threw about 45 pitches in a simulated game Saturday in Cleveland without a problem, putting him on track to rejoin the Tigers' rotation.
"I didn't feel it in the simulated game," Sanchez said. "Probably something was there after that, and I felt it today. But I don't know if it was like a re-injury."
His 35-pitch bullpen session Monday was prep work, not rehab, intended to ready him for 45-50 pitches Wednesday against the Twins.
"Just before I finished, probably three pitches before the end, I felt bad," Sanchez said. "I stopped right away."
Asked to compare it to his original injury, Sanchez said, "It's the same feeling. It's nothing different."
Andrews performed surgery on Sanchez for an injured labrum in 2007. Sanchez not only came back from that, he thrived, delivering at least 195 innings each season from 2010-12, and 20 more postseason innings during the Tigers' 2012 run to the World Series. He threw 182 innings in his first full season as a Tiger in 2013, leading the AL with a 2.57 ERA, before suffering an injury-shortened 2014 campaign.
Though Sanchez had a healthy season going until his rotator cuff strain in mid-August, he suffered through statistically the roughest season of his career, going 10-10 with a 4.99 ERA. His 29 home runs allowed lead the AL and are nine more than his previous career high.