Social media has been alive with debate claiming Mourinho is sporting the haircut to tease counterpart Pep Guardiola.
In 2014, Mourinho said of Guardiola: "When you enjoy what you do, you don't lose your hair, and Guardiola is bald. He doesn't enjoy football."
But Mourinho says it was simply a mistake that he now has no hair,.
"Sometimes I like to feel the cold weather and I like to change a little bit,' Mourinho told Sky Sports. "But this time was not the case.
"I fell asleep [in the barber's chair] and when I woke up it was so bad that I said to him 'bring the [number] one'. Hopefully, it will grow back again."