Must be wumming. If you ask Ronaldo to run 30 km, he can.He's still elite in short bursts but wow... his stamina is piss poor.
It's not about stamina, it's about his muscles endurance. 36 year old can't put so much strain to their muscles.
Pretty sure physios calculated his muscles strength and there are some data behind it.
The season is long, sometimes it's best to be very careful and not force injuries.