The Facts: Zylstra is believed to have suffered a serious and significant knee injury, sources tell NFL.com's Ian Rapoport.

Diehards Line: Zylstra will have more tests, but there isn’t a lot of optimism. Zylstra burst into the national spotlight last year with three TDs against the Panthers. Now, with Zylstra expected to miss six months, the path to workload for rookie TE Sam LaPorta is a little clearer.