QB Spencer Rattler is a strong candidate to start in Derek Carr’s absence, sources tell Garafolo and Rapoport

sfidc3 said
IMO, there is no such thing as co-QB anything, thats never worked. You start the QB who gives you the best chance to win, to me it’s obviously Rattler, we will see what happens….

I think he was just stating that Haener was the backup to Carr not because he was the better of the two but because you can only list one as QB #2.