Denver Broncos starting running back Montee Ball is sidelined with appendicitis.
Ball was scheduled for an appendectomy Monday afternoon.
Ronnie Hillman and C.J. Anderson shared snaps with the first-string offense at practice.
The Broncos haven't said how long Ball will be out, but it's a possibility that he'll miss the entire preseason.
In a tweet, Ball said, "I appreciate the get well wishes everyone! I will be ok and come back stronger than ever!!"
Ball, who set an NCAA record with 83 touchdowns at Wisconsin, assumed the No. 1 running back job this offseason. He was Knowshon Moreno's backup last year and ran for 559 yards and four touchdowns in 2013.