Manchester United boss Louis van Gaal will cross swords with fellow Dutchman and his former assistant Ronald Koeman on Monday – but both managers have declared their personal relationship to be "private".

Koeman, now Southampton manager, worked under Van Gaal at Barcelona but the pair fell out when they were at Ajax in 2004, when Koeman was coach and Van Gaal the technical director.

They shake hands on meeting now, according to Koeman, but Van Gaal referred to his former protege as “weak” in his autobiography and the closeness they once had never returned.

Van Gaal described Koeman as “a very good coach” but refused to talk about their relationship since the falling-out.

The United manager said: “I don’t have to describe my relationship with the trainer of the opponent... that’s more private. We play against Southampton and we have to speak about Southampton not speak about the coach.”

Koeman took a similar line, saying: “The game is Southampton v Manchester Untied and the game needs that attention and not the attention about both managers because that’s private.

“That was a working problem and I have to explain like that. It’s not an issue because it is eight or nine years ago and now I prefer to talk about the game.”

Asked about the relationship now, Koeman added: “Good. If we see each other we shake hands and that’s enough. He’s a great coach. He needs time, he will get the time of the club.”

United can go third if they beat Southampton, who are a point ahead of them in the table, and then face Liverpool but Van Gaal disputed suggestions the match against their Merseyside rivals was more important. He also believes the Saints can still be in the Champions League places at the end of the season.

Van Gaal said: “Southampton play better at this time and have more points at this moment than Liverpool so I think it’s good that we have to play Southampton now.”

Van Gaal also responded angrily to reports that he will be handed £100m or more to bring in new players. He added: “I think it’s disgusting always writing about numbers. I don’t think United executive vice-chairman Ed Woodward said anything about that, I don’t think I have said anything about that.

“It is disrespectful to my players and I don’t like to talk about it. I have to work with the selection I have and I have respect for my selection and I believe in my players.”

Wayne Rooney will be fit. The United skipper had a scan on Thursday to examine a possible knee problem but has been given the all-clear.

However record signing Angel di Maria will not be ready.

Southampton’s midfield options are becoming stretched at just the wrong time, with Jack Cork facing at least six weeks on the sidelines. The 25-year-old will not play again this year after sustaining ankle ligament damage in the Wednesday’s late 1-0 defeat at Arsenal.