If we could "unregister" him so he wouldn't count against salary cap limit then I don't think the club would have much problems paying him his wages to sit on the sidelines if we couldn't offload him. Money/liquidity is not our main problem, getting under salary limit is. But that's not possible. Players who were here last season must be registered again unless they leave. I think there are also possibilities to not register a player if he's longterm injured (6+ months) but maybe that's just for purpose of shirt numbers registration (because the club can only register 25 first team players) and his wages still count against salary cap, not totally sure about that. But Umtiti is fit to play now so we can't use that anyway.
Either way, no need to say the club has to pay player's wages as long as he's under contract whether he's registered or not otherwise this is a serious breach of contractual obligations.