Fred, Marcus Rashford, Luke Shaw and Diogo Dalot would have seen their previous contracts expire at the end of this season but United had the option to extend them by one more year to prevent them from walking away for free.
That option has now been taken up by the club which will give them enough time to negotiate longer term deals with the players.
The quartet would have been eligible to speak to foreign clubs and sign pre-contract agreements from January.
Rashford has been generating interest from Paris Saint Germain following an upturn in form this season.
The England international has scored eight goals in 19 appearances this season.
Dalot has made the right back spot his own this term, with the Portuguese international making 20 appearances across all competitions.
Shaw has made 15 appearances for Erik Ten Hag's side this term from his left back position.
Brazil international Fred has also made 16 appearances.
Manchester United return to action on Wednesday in the Carabao Cup against Burnley at Old Trafford.
The Red Devils are fifth on the Premier League table ahead of the top flight's resumption on Monday.
