Mack, who rushed for 1,204 yards in 2007, left Saturday's scrimmage early after his left Achilles' tendon tightened up causing him to hobble off the field.
While the tendon is a concern for Utah's coaching staff, especially after linebacker Kyle Brady ruptured his last season, Whittingham feels good enough about Mack to name him the starter.
Matt Asiata, Utah's JC transfer who broke his leg in the 2007 opener, continues to be sidelined with a sprained ankle. He injured the ankle last week and was expected to be out only a day or so. Now, a week later, he is only about 75 percent healthy according to Whittingham. He didn't participate Saturday.
Asiata missed most of fall camp in 2007 with a foot strain. That injury lingered longer than it was expected, much like his current ailment.
His absence has turned what was one of the most anticipated battles of fall camp into a frustrating situation instead. Whittingham said there was still a chance plans could change, but with the opener only two weeks away, feels time is too short for Asiata to get the necessary reps to be the starter.
"If you aren't on the field, you can't compete," he said. "No one feels worse about it than Matt, but the bottom line is he isn't ready for live reps."
While Whittingham hopes Asiata will be able to get some reps in Wednesday's scrimmage, Mack will probably get more rest than work in the coming days because he has proven himself and Whittingham would prefer to give his Achilles' tendon time to rest.
"It worries you because Kyle Brady had it last year, but this time off will be good," he said.
Mack had just three carries for eight yards in the scrimmage before he hobbled off the field. Most of the starters were held to limited minutes as the focus was put on settling rotations and getting the inexperienced would-be starters reps. Brian Johnson went 9-for-13 for 83 yards with a 5-yard touchdown pass to Bradon Godfrey. Backup quarterback Corbin Louks went 7-for-8 for 68 yards and Chad Manis went 3-for-4 for 18 yards.
John Peel led the receivers with four catches for 55 yards, followed by Freddie Brown with four catches for 38 yards and Jereme Brooks with four catches for 33 yards.
Freshman Sausan Shakerin led the running backs with seven carries for 39 yards and Ray Stowers rushed four times for nine yards. While the team improved from Tuesday's scrimmage to Wednesday's, Utah's offense continues to draw too many penalties.
Many of the penalties came courtesy of some smart play by the defense as it coaxed the offense offsides, Johnson said.
"They've been doing it for about two or three years now," he said. "You gotta expect the move call is going to happen and that the defense is going to try and bait you to jump offsides. The ref isn't going to be able to hear that when you have 110,000 people, so you have to be disciplined."
Utah at Michigan
Aug. 30, 1:30 p.m., Ch. 4
* The receivers make several nice plays from Jereme Brooks to veteran Brent Casteel and transfer David Reed. Brian Johnson should have plenty of options in 2008 with the group.
* Utah's punt returners have a hard time securing the ball, forcing the Utes to spend extra time on the drill.