Newcastle started the search for their eighth manager in 11 years after Sam Allardyce’s ill-fated reign came to a shock end after just eight months.
The 53-year-old looked to have survived the worst of the intense pressure which came his way as the Magpies’ season lurched from one crisis to another.
Confirming that manager and club had parted company by mutual consent with immediate effect, Mort said in a statement: “Mike and I would like to place on record our thanks for Sam’s efforts and wish him well for the future.
“A new manager has not yet been appointed at Newcastle. We will make a further announcement on the managerial position when appropriate.”
The news came as a huge surprise to Allardyce, who conducted his pre-match press conference for the United game earlier in the day.
In the official statement, he said: “I am disappointed to be leaving Newcastle, but I wish the club all the best for the remainder of the season and for the future.”