The Mariners scratched right-hander Taijuan Walker, their top prospect, from his scheduled rehab start Tuesday for Triple-A Tacoma because of what club officials termed arm stiffness.

Walker, 21, battled a sore shoulder in February that was eventually diagnosed as bursitis and prompted a one-week shutdown from all throwing in early March. He had not experienced further problems until Tuesday.

Plans called for Walker to throw 90-plus pitches Tuesday against Salt Lake at Cheney Stadium in what would have been his third rehab start. But he had trouble getting loose prior to the game, which prompted the decision to scratch him.