Sewell suffered the injury in Sunday's 50-point win over West Coast at Patersons Stadium and was subbed out in the third quarter.
Scans have since revealed a low-grade strain and minor bleeding, which will sideline him for one to two weeks.
"Brad had some awareness during Sunday's game and subsequently underwent scans that have shown he has a bit of bleeding in the hamstring," acting general manager football operations Chris Fagan said on Tuesday.
"Brad was able to jog lightly today, and depending on how quickly the injury site settles we expect him to resume playing within the next one to two weeks."
Sewell's absence makes way for former Geelong midfielder Jonathan Simpkin to make his Hawks debut after 31 touches for Box Hill on the weekend.
If Sewell fails to come up next week, he will miss the Hawks' trip to Launceston to meet Freo on April 20.
Brad Sewell is a midfielder in NAB AFL Fantasy. He averaged 88.86 points in 2012. Register your team at our AFL Fantasy Hub .
Jennifer Phelan is a reporter for AFL Media. Follow her on Twitter @AFL_JenPhelan.
