Spain's medical team revealed on Monday that they had found a grade two hamstring tear and that Morata could be out for over a month.
Antonio Conte, the Chelsea manager, claimed that Morata's withdrawal during the City game was precautionary, as the 24-year-old had suffered a knock in the Champions League victory over Atletico Madrid three days earlier.
I don't think it's a serious problem because he stopped before it will become a serious injury.More news: Analysts slam Khawaja Asif's India-related statement at Asia Society
However, in what will no doubt be seen as a hammer blow by the club's fans, the Spanish Football Federation tonight confirmed that Morata's problem is in fact much worse than was first thought, and that he has suffered a myofascial injury to his hamstring muscles.
Morata will now return to Chelsea, where he will be scanned again, but losing the record signing for any length of time will be considerable headache for Conte.
Tellingly, Conte opted to replace Morata with Willian against City which only increased theories that he does not trust Michy Batshuayi in big games.More news: Soccer fans injured after stadium barrier collapses at Amiens
Former Blues' striker Fernando Torres has praised Alvaro Morata's strong start to life at Stamford Bridge, proclaiming the Chelsea forward to be "one of the best" in the world.More news: Here's Where You Can Get Free Coffee On National Coffee Day