Both United and Manchester City, as well as Bayern Munich, have been linked with the Italy international this year.
Reports in Italy claimed United were considering making an 18million euros offer to sign Buffon in the January transfer window as they seek a replacement for van der Sar, who turns 40 later this month.
However, Juventus general director Giuseppe Marotta claims Buffon is going nowhere.
"I deny any negotiation with United, Buffon is a Juventus player," Marotta told Turin newspaper Tuttosport.
Buffon, who is under contract at Juve until June 2013, has been first-choice for both club and country since moving to Juve in 2001 but, at 32, has struggled with injuries in recent seasons.
He is currently out until the new year with a back problem.
Buffon's agent Silvano Martina also laughed off reports of Buffon's possible move to Old Trafford.
"These transfer rumours make no sense," he said. "Buffon has been sidelined for three months so who would want an injured player?
"Moreover, it seems to me that the best player at United so far has been van der Sar."