GLENDALE, Ariz. (AP) Brett Anderson, a projected starter in the Los Angeles Dodgers' rotation, will undergo back surgery and is expected to miss three-to-five months.

Anderson has a bulging disk in his lower back and was scheduled for an operation Thursday at a Phoenix hospital, Dodgers manager Dave Roberts said.

The back condition was diagnosed Wednesday, a day after Anderson felt discomfort when throwing to batters.

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''I was surprised, I was shocked,'' Roberts said before the Dodgers' exhibition opener. ''We didn't think our depth would be tested so early.''

A 28-year-old left-hander, Anderson was 10-9 with a 3.69 ERA last season. His 31 starts and 180 1/3 innings were both career highs.

While with Colorado in 2014, Anderson was injured during a start on Aug. 5 and had season-ending surgery for a herniated disk in his lower back.

He agreed to a $10 million, one-year contract with the Dodgers in December 2014 and accepted a $15.8 million qualifying offer from Los Angeles last November.