ENGLEWOOD — Denver Broncos starting running back Montee Ball is sidelined with appendicitis and isn't expected back until the AFC champs' opener against Indianapolis on Sept. 7.
Ronnie Hillman and C.J. Anderson shared snaps with the first-string offense at practice Monday and are expected to get the bulk of the work in Ball's absence this month.
"I appreciate the get well wishes everyone! I will be ok and come back stronger than ever!!" Ball tweeted Monday shortly before he was scheduled for his appendectomy at a Denver hospital.
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.
"Luckily it's early in camp and it'll give him a chance to come back," Hillman said.
Ball's strong second half helped the Broncos decide to let Moreno leave in free agency. Moreno signed with Miami.
Coach John Fox said Ball started feeling sick Sunday during the Broncos' day off "and of course came in today, again, not feeling very good." Fox said the good news was that the organ didn't burst "so it was really a blessing that we caught it now."
The Broncos have little doubt that Ball will be able to resume his role as the Broncos' lead back upon his return.
"I'm not into predicting the future, but he's really grown a lot as far as his understanding of the offense and execution of all parts of his job," Fox said. "Knowing what kind of guy he is, he'll work at it and mentally he'll stay on top of his game and then when he comes back physically, we'll wait until he's ready."
Ball's absence means Hillman, Anderson and a host of undrafted free agents, led by Duke's Juwan Thompson, will get more carries in their quest for a roster spot.
"You hate to see anything happen to a player, whether it's an illness or an injury on the field, but sometimes when a door shuts, another door opens," Fox said. "So, it'll give us a chance to get those young backs in there and hopefully they can grow and progress."
None of the Broncos' running backs have ever started an NFL game, although Hillman has the most experience with 25 career appearances despite getting benched over the last half of last season.
Although many see him as more of a change-of-pace back than a workhorse like Ball or even Anderson, Hillman's renewed focus on football during the offseason has made an impression.
"I've seen great growth," Fox said. "I think he's been a different guy in those meeting rooms. I think with a full offseason this year and him attacking it the way he did you're starting to see the benefits of that here on the field."
Running backs coach Eric Studesville was equally effusive in his praise for Hillman.
"I love what Ronnie has done," Studesville said last week. "From when we started this spring in April forward, he has been unbelievable. He's a completely different guy in the best possible way and I'm just excited about what he's doing, how he's approaching it, how he's making plays on the field. It's been great. It's been there the whole time, but we're finally seeing the maximum side of it."
Hillman said it's basically just an attitude adjustment, and "we're about to see how well it's paying off."
Anderson also has turned heads during camp after trimming down following a sluggish minicamp and OTAs. Asked what was different about him from a year ago, he said, "I know the playbook now and that makes me play faster."
At 5-foot-8 and 224 pounds, Anderson is squatter and thicker than Hillman (5-10, 195) and shows great leverage on blitz pickup like he did in Saturday's scrimmage when his block of linebacker Nate Irving allowed backup quarterback Brock Osweiler to escape.
This ability could get him significant preseason snaps with Peyton Manning.
"No matter if it's me or Ronnie in the game, with 18 we don't miss a beat," Anderson said. "So, we're going to keep this thing going."
Notes: WR Emmanuel Sanders (strained right thigh) and CB Tony Carter (groin pull) were among the new names on the Broncos post-practice injury update.
Follow AP Pro Football Writer Arnie Melendrez Stapleton on Twitter:http://twitter.com/arniestapleton