Chicago Cubs starting pitcher Cole Hamels has reportedly been dealing with “shoulder fatigue,” and will not make his scheduled start on Friday against the St. Louis Cardinals. Right-hander Alec Mills will start in his place, according to Jesse Rogers of ESPN:

After losing to the Cincinnati Reds last night, the Cubs fell three games back of the St. Louis Cardinals in the National League Central Division entering a four-game series against the Redbirds on Thursday night. They will line up Kyle Hendricks, Mills, Jose Quintana and Yu Darvish as they look to gain ground on the Cardinals in the Central.

Hamels has repeatedly said that he has felt healthy since returning from the injured list at the beginning of June, but he certainly has struggled of late. The veteran left-hander has not made it past the fifth inning in his last three starts, and twice has not made it through four innings.

After looking like Chicago's ace prior to the All-Star break, Hamels has had a brutal second half. In nine starts, Hamels is 1-4 with a 6.39 ERA and a 1.974 WHIP. Meanwhile, opponents have a .949 OPS against him, and his walk rate has risen significantly.

Cubs broadcasters Len Kasper and Jim Deshaies have noted that Hamels has looked a little more rushed in his delivery, and that the frustration has been more noticeable.

This is hardly the best timing for the Cubs to be skipping a turn in the rotation. However, Mills has been used as a spot starter multiple times this season, and will try to deliver a quality start on Friday.