Withrow's injury could be more serious, as he had back stiffness the day after his first bullpen session. It's a recurrence of a chronic problem that has contributed to his slow progression. Withrow, a first-round Draft pick in 2007, received a $1.35 million bonus.
Withrow, who is not expected to make the Major League staff this spring, ended last season on the disabled list with shoulder soreness and had a stint in the Puerto Rican Winter League canceled when he and his wife were involved in an auto accident in which their car flipped.
He was sidelined for three weeks with body soreness, but said he began his winter throwing program as he normally would in early December. He also participated in the Young Guns minicamp two weeks ago.