People are just guessing 3 weeks because that's the average time for a hamstring injury. Scans aren't until tomorrow, we wont know anything for certain until then
Didn't Alba and Xavi recover from hamstring injuries they got last week? And it didn't look to serious to me. Hopefully, he'll be back for the second leg.
I think it's not a serious injury. He even ran after it happened and looked pretty good overall. I was surprised to see him subbed off, but there's no point in playing an entire half with a hamstring injury, even a lighter one.