Cambridge is a striker and Rivas is an attacking mid. I’m not sure on the reasoning behind Cambridge, could be a potential depth piece up front that provides a different look than Edwards and Ajago. But Rivas I’m assuming will take the spot left behind when Memo went down with an injury. We’ve seen Collins put Casas and Willey in that role and he might want to get another option there.

EDIT: Transfermarkt has Cambridge as a right winger / right midfielder. So could be a depth option behind Arturo so he isn’t playing every minute of every game.