I think fitness wise, it will be hard (anyone who misses Pre Season usually takes a while/if at all that season) to get the same level of fitness, but on a plus side, he will be back to 'fitness' work in 3-4 weeks.. so by round 5 he should be good to come back..
I think Ryder can handle sole ruck duties fine and seems to relish that full time gig, looking at the line up:
Rnd 1 up against NM could be ok.. Goldie is a great ruck, but he works 1 out.. so Ryder won't be run off the park
Rnd 2 is Hawthorn who struggled last year, but have got McEvoy in to try and address their issues at ruck.. with Roughie set to go forward to cover Franklin.. Ryder should be able to handle McEvoy and Hale and has done so before. Especially considering we are catching Hawthorn early in the season where they 'may' be struggling with Premiership hang over and a shorter pre-season.
Rnd 3 is Carlton who still use Kruezer predominately.. who is better as a 'tall mid' rather than 'big man'.. Ryder has and should match up well in this game. Fatigue could be a factor with Carlton also able to use Warnock and Hampson (depending on injury)
Rnd 4 against Freo 'could' be a problem if Sandi, Griffen and Clarke are all healthy, or two out of three are healthy, however 1 out against Clarke should see Ryder be able to 'break even' with similar game styles. Fatigue liklely to be a huge problem for this game as it is at a big ground, PS, and likely high heat (even though it is a night game).. and if there is a tag team of Clarke and Sandi, then Ryder could struggle. Potentially dangerous game. I would suspect the fitness staff would be looking for every advantage to try and get Belly ready for this clash, even if for 'half' before being subbed.
Rnd 5 against St Kilda is no problem, one being they don't have a ruck after trading McEvoy for long stints.. however it is expected that Belly will be well and truly back for this game.
So I think Rnd 4 will be the big worry for the coaching staff right now (not that ANY of these games are 'easy' but I don't see Ryder being smashed in any of them).