Yeah, I hope it's not too bad. In football the teams usually do a MRI immediately to confirm if it's an ACL. I guess there could be a lot of swelling but I don't know why you would wait to do a MRI if it's something very serious.
ACL injuries are pretty easy to diagnose w/o MRI, so early reports that it sounds bad ... that's not good. Of course they MRI to confirm, but darn.