JUPITER, Fla. (AP) — St. Louis pitcher Chris Carpenter has returned to the Cardinals’ spring training camp, with manager Mike Matheny still unsure when his ace will be back on a mound.

Carpenter, who has yet to pitch in a spring training game, underwent four days of tests last week in St. Louis to determine the cause of a nerve ailment that has weakened his throwing shoulder. Matheny thinks the right-hander will have to rest.

The 37-year-old has not faced hitters since batting practice on March 3. A bulging disk in his neck originally was thought to be the cause of the problem.