Fernandes' outstanding performances have helped United reach the top of the table at this stage of the season for the first time since 2013.
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In December, the 26-year-old made six Premier League appearances and scored three goals as United remained unbeaten, recording four wins.
Fernandes, who joined United from Sporting CP in January 2020, won the award for the first time in February.
With football across the world in a coronavirus-enforced lockdown from March until May, he retained his award in June as he helped United climb the table to finish the 2019-20 campaign in third place.
The Portugal international won the award for a third time in November before retaining it the following month.
His four wins bring him level with compatriot and former United attacker Cristiano Ronaldo -- as well as stellar names Dennis Bergkamp, Thirerry Henry, Frank Lampard, Paul Scholes, Alan Shearer and Jamie Vardy.
The award was first introduced in the third Premier League campaign and the first recipient was former USMNT manager Jugen Klinsmann in August 1994, while player with the most wins is Manchester City forward Sergio Aguero with seven.
Tottenham's Harry Kane -- who claimed the award three times in 2017 -- and former Liverpool midfielder Steven Gerrard have six each, while former United forwards Robin van Persie and Wayne Rooney both won the award five times.
Liverpool forward Mohamed Salah was the first player to win the award three times in a single season -- in the 2017-18 campaign. Fernandes will match that record if he wins the award once more this term.