Gragg, a sophomore, got caught in a pileup during Arkansas' scrimmage in Reynolds Razorback Stadium and had to be carted off the field.
"I feel bad for him," Petrino said. "He's worked extremely hard. I'm sure it will be a situation where he'll have to have surgery and be out for the year."
Gragg was expected to play a bigger role in the offense after catching one pass for 25 yards as a true freshman in 2008. The reception came on a critical fourth down play against Louisana-Monroe.
"We're going to go call him and send him a couple text messages, make sure he's OK," Arkansas quarterback Ryan Mallett said.
Gragg's injury also thinned out a position already missing tight end D.J. Williams, who sat out his second practice with an ankle injury. Petrino said Williams' injury isn't severe, but wasn't sure when the team's top returning receiver will practice.
Petrino said Arkansas won't rush Williams back on the field because he knows the offense.
Junior Ben Cleveland — who returned to practice Tuesday after missing Tuesday's workouts with a neck stinger — and senior Joseph Henry handled the bulk of the work without Williams and Gragg.
Henry caught two passes, including a 17-yard touchdown from Mallett. Cleveland caught one ball for 22 yards, hanging on despite a jarring hit by safeties Anthony Leon and Tramain Thomas.
"I just curled up in a ball and said a little prayer and the Lord blessed me right there with that big ol' man (Leon) out there," Cleveland said of the play.
Hogs Lose Gragg To Ankle Injury
Hawgs Daily Top Stories
Scout On the Road: SeptemberScout takes a look at some of the top prospects we saw in person during the month of September...
Scout FootballYesterday at 2:00 PM
Longhorns Preview Oklahoma StateTexas offensive players discuss the Longhorns' upcoming game at Oklahoma State to kickoff Big 12 Conference play.
Horns DigestMonday at 6:21 PM
Louisiana CB 'Real Close' to a DecisionIt may not be too long before one of the top cornerbacks in Louisiana makes his decision. Four schools are high on his list and you can get the latest here...
Scout FootballMonday at 6:15 AM
JC defensive back talks ISU official visitOver the weekend, Iowa State played host to one of their top 2017 targets in the current recruiting cycle in Paramount, CA three-star JUCO CB Keisean Nixon. This visit for the…
AllCyclonesSunday at 6:34 PM