The Ecuadorian, who joined Manchester United back in 2009, missed the majority of last season due to an ankle injury and has failed to impress supporters since the retirement of Sir Alex Ferguson in 2013.
Under Mourinho, however, Valencia has undergone something of a regeneration, producing a series of powerful, solid performances at right back.
Crooks included Valencia in his Team of the Week on the BBC following his performance against AFC Bournemoutth, tipping the 31-year-old to be an influential member of the squad under Mourinho.
“Valencia was always Manchester United’s outlet against Bournemouth in a frightfully tight first half, when space was at a premium,” he wrote.
“But you can always depend on him to retain the ball under pressure and he did it at a time when United needed it most.
“The Ecuador international has been playing the game a long time and has served United well over the years.
“However, I suspect that for all of Mourinho’s multi-million pound signings, it is Valencia – bought by Sir Alex Ferguson seven years ago – who might well prove to be one of his most important players.”
The antipathy towards Valencia in recent years has always been hard to understand. In a world where footballers are prone to throwing their toys out of the pram at the hint of any slight discomfort, the Ecuadorian has always been a dedicated, reliable presence on the pitch. Week in, week out he is there, ready to give everything for his side, regardless of what role he has been asked to play.
And against Bournemouth his influence was crucial. With Juan Mata often moving infield from right wing, Valencia acted as a potent force on the right hand side, offering attacking impetus and defensive stability in equal measure.
He may not grab the headlines, but the silent, stony faced Ecuadorian is just as crucial to Mourinho as any other player, and Man United fans will hope he remains injury free over the campaign.