The 24-year-old is facing up to 10 weeks on the sidelines after collapsing during Saturday's win over Gold Coast at Aurora Stadium in Launceston.
Rioli was sprinting for the ball in the final quarter when he felt a twinge in his left leg. It's the same hamstring he injured against the Swans in round eight which saw him miss three weeks.
"Unfortunately scans have indicated that Cyril has sustained a hamstring tendon injury, which is more serious than we first anticipated," Hawthorn football operations boss Chris Fagan said.
"While he is understandably disappointed to be missing some footy, he is eager to begin his rehab with the aim of making a valuable contribution to the side again this season."
Rioli had hoped his latest injury was minor when he spoke earlier on Sunday.
"It felt pretty similar to the one I did against Sydney. So fingers crossed it's the same [amount of recovery time]," he told the Hawks’ website.
"The leg is feeling really sore. After I iced up it seized it up a bit. I'm definitely going to ice up over the next few days and inspect the injury and hopefully I'll be back after the split round."
Like North, the Hawks have been hit with injuries to key players this season. Sam Mitchell is listed to return in about a week but could play against the Roos on Friday night.
