This is Mourinho's way of challenging his most talented players. Some players don't respond well to it and some do, but no doubt Dele needed to be challenged. The players he has dug out in the past are all a certain type of player, Ozil, Hazard, Martial, Pogba, Ndombele, they think they have a right to play because of their immense talent but they don't. They think because of their talent they need to be indulged and can take it easier than their less talented teammates.
Look at where Hazard is now. He's a fat lump collecting a huge salary from the Real Madrid massage table. Mourinho was right about him. Look at Pogba and Martial, how inconsistent and lazy they still are. Look at Ozil exiled from the Woolwich squad.
Dele did OK in the first 45 minutes against Stoke. Just OK. Is that enough to get carried away and start doing his dumb flicks at 1-0 up away in a quarter final? Mediocre players like Lucas don't get castigated in the same way because Mourinho knows they don't have the talent to give much more. Dele does, he has shown that in the past. His talent didn't just disappear.
He will almost certainly leave the club in January because he doesn't understand his circumstances, he doesn't understand that he only stayed in the team the last 2 seasons because Poch went soft in the head. Eriksen and Rose were in the same situation, playing shit and living off the past and Mourinho threw them out immediately. He was given a second chance because he's got huge talent and is still young, but he hasn't shown any self-awareness. He seems mystified by his absence from the first XI but it is not a mystery. Lamela came on after 2 months out and looked much livelier than him, how can Dele explain that? Feeling sorry for yourself is not a good excuse.