Being a grade 3 tear, (the worse you can get according to JR8 himself), I reckon both surgery and rehab were options that were put on the table and Jack and the club have taken an educated risk on rehab in the hope it gets him back to playing this year. 8 weeks would be minimum I reckon although my Google friend ;D seems to indicate closer to 12 weeks. The risk is that rehab doesn't work and then surgery & 9 to 12 months await.
Hope for best, prepare for the worse is my motto.
Think it would have been a similar discussion to that of Daniel Wells, below :
"Surgery was an option but this course firstly allows Daniel to make a full recovery and, secondly, keeps alive the possibility of a return to playing in 2019," Collingwood football manager Geoff Walsh said.
"The recovery has to be strong and a priority, which it will be, but Daniel has the prospect of playing again to aim for."