One week after he fumbled while trying to dive into the end zone, Hillman was stripped by linebacker Alec Ogletree after catching a swing pass from Peyton Manning in Saturday's 27-26 preseason win over the St. Louis Rams.
Fox said despite the fumbles, he hasn't lost faith in the second-year pro.
"I personally thought his progress was stopped; otherwise he's got to get on the ground faster or do a better job of holding onto the ball when guys yank on him late in the down," Fox said. "Again, every one of these things is a learning experience for these guys. I think he will work on it, so I have not lost confidence in him whatsoever."
With Knowshon Moreno's improved play and the expectation that rookie Montee Ball's role will expand as he gets a better grasp of the blocking scheme, Hillman conceded that his fumbles might cost him playing time.
"Definitely, when you put the ball on the ground, and you have guys like Montee and Knowshon running the ball as well as they did tonight and Lance (Ball) -- it kind of affects your competition," Hillman said. "It's unacceptable -- what I did, and I just have to work on it."