Probably a standard grade 1 hamstring but when it happens to someone with a history of hamstring strains they generally add a further week or two.
I know Looney had mainly knee issues at brisbane but I'm pretty sure he pulled a few strings as well from memory.
The Hawthorn game is 13 days post injury.
The Brisbane game is 20 days post injury
The Carlton game is 28 days post injury
The Adelaide game is 34 days post injury
Hopefully he is back for round 3, but I reckon given his importance to the team and his injury track record that we will see him return for the Adelaide Crows game, all things being equal .