I just watched the end of the 1st half on the NRL site. The last play of the half sees Brett pick up a very loose offload and he is tackled by a saints guy I don't recognise. This tackle has no knees and is pretty soft. Earlier, at 37:58, Brett takes a bomb and is tackled pretty hard by Nightingale. The knees could have been in this tackle. Brett seems to get up fine from both tackles. Tooves says the injury was obvious once he cooled down at half time, so hard to say when it happened.