I’m going to go with more serious.
Consider that the registrations are, unless I’m much mistaken, for the group stages only. The last group stage matches take place on the 2nd of November, which means that if he picked up a rather serious injury, for which we expect him to be out for a significant amount of time, there’s absolutely no point registering him, if we need the space for someone else, which we do, since we have already registered the maximum 17 non-homegrown players.
Even if he was off on a free transfer next summer, there’s absolutely no reason to not use him when we can.