The former Chelsea manager was appointed as Louis van Gaal’s replacement in May after the Dutch coach led United to a disappointing fifth-place finish last term.
Mourinho signed Villarreal defender Eric Bailly, former Paris Saint-Germain striker Zlatan Ibrahimovic, Borussia Dortmund midfielder Henrikh Mkhitaryan and Paul Pogba in a world-record £89m deal from Serie A champions Juventus.
United won their first piece of silverware under their new manager in August when the Red Devils eased to a 2-1 win against reigning Premier League champions Leicester City in the Community Shield at Wembley.
Mourinho’s side are in sixth place in the Premier League table but six points behind current leaders Manchester City after seven games.
Former United striker Yorke has set a timeline for Mourinho to achieve success at Old Trafford or else face an uncertain future at the club.
“He will not stop working until he has achieved something but I think he needs to bring some silverware in by 18 months into the job,” said Yorke, speaking exclusively to 888sport.
“He will be given a year to cement his side but that’s about it. Then he needs to produce the goods because it’s been four years since we won the Premier League and for a club the size of Manchester United that is not acceptable.”
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