Cubs C Castillo out with lower-back tightness

CHICAGO (AP) Mike Olt is hoping his work in the minors will produce more success in the majors.

Olt was recalled by the Chicago Cubs on Friday after a two-game rehab stint with Class A Kane County for a strained left hamstring. The rookie slugger, who was acquired in the July 2013 trade that sent Matt Garza to Texas, was hitting .139 with 12 homers and 30 RBIs when he was sent down to Triple-A Iowa on July 22.

''I had to go down and make a physical adjustment,'' he said before Chicago's game against Pittsburgh. ''What I was doing up here wasn't working and you know you get into a funk and went down there and changed my swing a little bit. Made it so it's a little more simple.''

Olt, 26, batted .302 with seven homers and 24 RBIs in 28 games with Iowa. With All-Star Anthony Rizzo sidelined by a strained lower back, Olt could see a lot of time at first in addition to his usual position of third base.

''I think he'll play obviously some first base and then we'll take it day to day, see how his legs are doing,'' manager Rick Renteria said, ''and continue to mix and match the rest of the guys.''

Olt was available for the series opener against the Pirates, but catcher Welington Castillo was scratched due to tightness in his lower back. He is day to day.

John Baker replaced Castillo in the lineup, and first baseman Chris Valaika moved up from the eighth spot in the batting order to No. 6.