So far there has been no further confirmation from Madrid regarding Bellingham illness. I read on the club official website that Bellingham did not participate in the training session because he had a stomach ache. The good news is that Vinicius Jr and Arda Guler have joined the training session, this is good news for Ancelotti. If Bellingham is really absent, this will really give Ancelotti a headache, because Bellingham has been a key player so far. However, I have a feeling that Bellingham will be able to play in the derby match against Atletico, because the England national team player is not injured but only experienced stomach ache.
Real Madrid actually need to give Jude Bellingham some time to rest because he played too much recently for both Real Madrid and England. He is young and can recover quickly but sometimes they must give him some time that is necessary to recharge energy. The season is long enough and Real Madrid need Jude Bellingham for a long season, not only in a single match or a few weeks. Avoiding injuries to have an important player during a long season is more important and with the latest news about Jude, he deserves to rest a few days.
So far, Madrid can still win even though they are not supported by a number of important players Thibaut Courtois, Arda Guler, Eder Militao and Vinicius Jr. I predict that the derby match will be won by Los Blancos, even though it is a narrow victory.
Real Madrid actually have better form than Atletico Madrid even they did not have some important players in latest matches. They can continue their good form without Jude Bellingham and I believe Carlo Ancelotti can have good alternative solutions for a squad without Jude.
I actually think that Real Madrid should keep Jude Bellingham on the substitute bench. They should start the match against Atletico Madrid without him. If the situation gets really tough, they can, of course bring him on. But if they can win without him, which I think is possible for them, they should not play Jude Bellingham in that match in my opinion. Because it is true that Jude Billingham is playing really well for them. It is also true that the fans also really love him already. But it is never going to be good for him or even the squad if he cannot stay fit to play.
Anyway, even though I don't think the injury is really serious, I also do not think that they should take this lightly. After all, he is the best player for them at this moment.