If Forest do indeed park the bus next week as expected, then Onana becomes less essential anyway. Put someone like Luiz or Barkley in there, someone who can join and contribute in attack and also pick forward pass if the movement is right. It might make us a bit more exposed on the break, but I'd have faith that Youri + luiz/barkley with Rogers in front would create enough chances for us to score a couple.
Given his record with 'niggles', I'd be surprised if we see him before Burnley, possibly even Liverpool.