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
Hogs fueled by 2016 collapsesArkansas is using its collapses against Missouri and Virginia Tech as fuel this offseason.
Hawgs Daily1:38 PM
Diamond Hogs are consensus top-25 teamCheck out where the Diamond Hogs are ranked after two weeks of SEC play.
Hawgs DailyYesterday at 1:33 PM
5 questions heading into spring practiceThese are five things to keep an eye on as Arkansas begins spring practice Tuesday.
Hawgs DailyYesterday at 1:22 PM
Fortune cookie, Bielema deliver good newsA phone call from Bret Bielema and a fortune cookie was all it took for Gabe Richardson to get some great news on Monday night.
Hawgs DailyYesterday at 10:39 AM