Simple
Have him get "Injured" at Royal Rumble and say he is out for a while, don't mention him on TV or anything..
Mania Hogan in ring and Rusev comes down and threatens to attack him, challenging him to a match. Just before attacking Hogan the music hits and Cena comes out and takes out Rusev leaving him laying in the ring for Hogan to pin.
Hogan gets one more Mania moment, Cena stopped the unbeatable Russian fans cheer..
I'd be ok with this and get behind it as it goes with my prior mentioned comment about having him feud with Rusev.
But, unless it's a real injury, there is no way they sit Cena for a few months during the height of Mania season. Like the guy or hate the guy, he is still their most marketable superstar and gets great crowd reactions. Can't keep him away for a fake injury for that long.