United travelled to the San Siro in the quarter-finals of the competition in 1999 on their way to winning a famous Treble.
The Red Devils took a 2-0 lead from the first leg to Italy, courtesy of a Dwight Yorke brace.
Inter, however, did possess the best striker in the world in Ronaldo, while Diego Simeone was ready for a fierce midfield battle with Keane.
But Keane did not care too much for the duo, walking straight past them as they adjusted their socks while the players were exchanging handshakes.
The reaction of Ronaldo and Simeone remains priceless to this day, while Keane is still pretty terrifying.
A late goal from Paul Scholes, meanwhile, saw United draw 1-1 with Inter, and we all know what they went on to achieve.
CLASSIC: When Roy Keane mugged off Diego Simeone & Ronaldo. No nonsense. 😂👏 pic.twitter.com/I2Hf0xYtV6
— SPORF (@Sporf) December 4, 2016
Liverpool fans will be drooling over Naby Keita.
Roberto Firmino’s no-look finishes are brilliant.
When A-League goes Sunday league.
Jack Stephens got more than he bargained for.
What a Sunday afternoon.
Jose has been at it again.
Some fine play from the pair.
A different take from the United legend.
Mohamed Salah has made a lot of people very happy.