The Cardinals said Saturday that the right-hander had stopped throwing following the results of an MRI a day earlier.
Motte pitched an inning against the New York Mets on Thursday in Port St. Lucie, then told the team his forearm tightened up on the bus ride back to the Cardinals' spring training complex.
"We're certainly going to be as aggressive as we can with the rehab, but in terms of DL, I would say that's likely going to happen,'' general manager John Mozeliak said.
Motte was 0-0 with one save and a 5.00 ERA in nine innings during spring training.
Setup man Mitchell Boggs will move into the closer's role.