Janssen agreed a new two-year deal at the end of the last campaign, but he has now accepted a media role back in North America.
Panthers’ boss Corey Neilson said: “You get curve balls in sport and this one is up there with the best.
“Cam’s a great guy and he was as good as in tears when he told me what had happened, but he’s landed a big job with a sports network on FM radio and will also be working with his beloved St Louis Blues.
“We’re not the first team to lose an important signing late in the summer, and we won’t be the last.
“It’s happened to us before – it happened last summer and we ended up getting Cam as a replacement then, so it will, as ever, be onwards and upwards and we’ll get on with it.”
(Image permission: Karl Denham)