Yes he is. Nwoko is going to play sparingly. L usually doesn't lean heavily on freshmen and Nwoko hasn't done much in these games in France.
Walker was the backup 5 last year and is not any bigger than Casey. When Omier went down in the ACC tournament, we played Casey at the 5 for long stretches.
The only other option is Cleveland, but those would be tiny lineups. We had some good minutes with Miller at the 5 in the elite 8, but I don't think that's something L will want to do very often this year.