Kennedy will have to wait until West Coast unfurl their premiership flag in round two against GWS to play his 200th game for the club.
“I just needed a green light and I would have played him (Kennedy), and he would have played. But we have to listen to the medicos and back in the system,” Simpson told reporters on Thursday.
“It’s always a challenge when you get an A-grade talent like that and what risks are you willing to take.
“I was willing to take a few risks but we have to back in the collective and the decision was we’re not going to play him.”
Fellow forward Jamie Cripps is another out from last year’s grand final win against Collingwood due to off-season foot surgery.
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Willie Rioli is expected to join his premiership teammates on the sidelines after suffering a foot injury on Wednesday at training.
The 23-year-old is awaiting scan results but is unlikely to take on the Lions.