Prior was limited to nine games last season by shoulder problems and pitched only 10 1/3 innings in spring training. The Cubs said Prior is scheduled to visit orthopedic specialist Dr. Lewis Yocum in California for further evaluation.
Prior was optioned to Triple-A Iowa at the end of spring training, then put on the minor league team's disabled list.
He pitched Thursday in Mesa, where the team has its spring training and minor league headquarters.
An 18-game winner in 2003, Prior has been plagued by injuries the last three seasons.
He signed a one-year deal worth more than $3.5 million dollars during the offseason.