Florida's depth chart at running back looks like this: a career backup, a walk-on and a former safety.

With a beefed-up offensive line and a few new faces in the backfield, the 10th-ranked Gators were supposed to have an improved, maybe even feared, ground game this season.

But with starter Matt Jones sidelined because of a viral infection and freshmen Kelvin Taylor and Adam Lane continuing to have ball security issues, Florida's rushing attack is alarming for all the wrong reasons.

"Any time you have something like this and you're in uncharted waters and you're uncertain of it, you always plan without the player," coach Will Muschamp said. "If the player's there, it's great. That's gravy for everybody."

It's unclear when Jones will return.

The 6-foot-2, 226-pound sophomore was diagnosed early this month, lost what several teammates called significant weight and has missed nearly three weeks of fall practice.

Jones had blood work done Monday, Muschamp said, and is working out regularly. But getting no on-the-field work is making it more and more likely that Jones will miss Florida's Aug. 31 season opener against Toledo.

"All I know is he is progressing very well," Muschamp said. "I get a daily update. He feels good. He's doing more and more every day from a workout standpoint, and that's all I know. We're playing it by ear, and every day we have a staff meeting, we have an injury report, and he gives me an update."

Without Jones, the Gators have turned to Mack Brown, a fourth-year junior who has carried 40 times for 167 yards in three seasons. Brown was a highly regarded recruit in 2009, but has been one of the program's biggest disappointments since.

"At running back, you need a certain amount of reps to stay in the groove," Brown said. "I didn't get that many reps the last couple years. It was kind of tough sometimes. ... I don't regret nothing really. I met a lot of good teammates. I played for great coaches. Things happen for a reason."

Florida also has walk-on Mark Herndon, who was awarded a scholarship Tuesday, and former defensive back Valdez Showers in the mix.

Taylor, the son of former NFL running back Fred Taylor, and Lane were supposed to rise up the ranks and push for playing time this season. But the newcomers have failed to impress the coaching staff.

"No. 1 is ball security," Muschamp said. "You've got to take care of the football. That's the No. 1 thing. They're very talented runners, but so much more goes into it other than just running the football. They've got to take a step. Very pleased with both guys. They're going to help us this year. How much, their role, will depend on how they continue to develop."

The Gators ranked 39th in the nation in rushing last season, averaging nearly 190 yards on the ground. Mike Gillislee (1,152 yards) became the first Florida player since Ciatrick Fason in 2004 to top 1,000 yards rushing in a single season.

Many believed Jones would repeat the feat in 2013, especially with three offensive linemen — center Jon Harrison, guard Jon Halapio and left tackle D.J. Humphries — returning and anchoring a unit that also includes experienced transfers Max Garcia (Maryland) and Tyler Moore (Nebraska).

Muschamp's philosophy is to wear opposing defenses down on the ground, a run-oriented attack that works best with a big back like Jones.

And until he returns, the Gators realize they have to find creative ways to fill the hole.

"Matt's obviously a powerful runner and brings that identity in the run game of being physical," offensive coordinator Brent Pease said. "So the other guys have got to pick that up. We're not going to change our identity. They have to change the void on that."