The Red Devils will make the short trip to Merseyside in the opening game of the Premier League weekend following the conclusion of the international break.
Understandably, some Liverpool and Manchester United players would have been involved in the same national team squads over the past fortnight ahead of the Premier League’s return.
Indeed, Reds captain Jordan Henderson and Alex Oxlade-Chamberlain played alongside Manchester United duo Jesse Lingard and Marcus Rashford during the international break.
Stam was part of the Manchester United team for two seasons as he won two Premier League titles, the Champions League and the FA Cup before leaving for Lazio in 2000.
And the retired Dutch defender, who is currently in charge of Reading, warned the Manchester United players that their friendships with some of the Liverpool squad must be cast aside for the bitter derby.
“Nowadays a lot of players are good friends so it might be quite friendly in the tunnel,” Stam told Sky Sports News.
“When we played a lot of the time it was quite different. Something happened in the tunnel occasionally over there.
“But it’s all about rivalry, the way I look at it when you go into that tunnel there are no friends.
“There are rules but some rules are there to be broken occasionally to do everything to get that result.”
Liverpool played out a goalless draw with Manchester United in the Premier League at Anfield last season before a 1-1 draw between the two rivals at Old Trafford back in January.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news