The 18-year-old is considered one of the brightest prospects in the club’s youth academy but needs experience of senior football.
And, according to The Sun, Mount will spend next season on loan at Chelsea’s feeder club.
Mount will also gain experience of European football during his spell in Holland because Vitesse finished fifth in the Eredivisie last term to book a spot in the Europa League.
Mount, who joined the club at the age of six, is under contract until 2021.
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He wrote on Instagram: ”Pleased and thankful to have signed a new 4 year contract with @chelseafc.
“It's been my home since 6 years old and I'm honoured to be part of the club.”
Mount skippered Chelsea’s Under-18s to the FA Youth Cup final last season and got his hands on the FA Youth Cup and UEFA Youth League.
His profile on the club's official website reads: "He has always been an attacking midfielder, capable of playing in any of the central midfield roles and is particularly strong at going from box-to-box.
"He has scored a lot of goals at schoolboy level but is also a good tackler."