Foulkes was a survivor of the Munich air disaster in 1958 and went on to become a stalwart at Old Trafford, making 688 appearances for the club.
The former defender made his debut in 1952 and sits fourth on the club's all-time appearances list, with only Ryan Giggs, Bobby Charlton and Paul Scholes having represented United more.
United's executive vice-chairman Ed Woodward paid tribute to Foulkes, saying on the club's official website: "Bill was a giant character in the post-war history of Manchester United.
"He was a very gentle man, who I was privileged to meet on several occasions, including most memorably with his team-mates at the Champions League final in Moscow, 50 years after his heroics in the Munich air crash.
"Bill's contribution over almost 700 games and nearly 20 years will never be forgotten. The thoughts of everyone at the club – directors, players, staff and fans – are with Bill's family."
Foulkes, who spent his entire playing career at Old Trafford, started in United's 1968 European Cup final win over Benfica at Wembley and was a member of the squad that won four First Division titles.
