From the Guardian (https://www.theguardian.com/sport/2017/jan/21/eddie-jones-sees-a-bright-future-with-sherylle-calder-in-england-camp):

I'm a bit disappointed that it won't be May and Watson starting, but perhaps it's an indication that Watson will be looked at at fullback? Either by starting on the left wing and moving to fullback to make way for May later in the game, or coming off the bench at fullback. Or is it simply that Jones thinks Nowell is the first name on for a wing berth?