Van Dijk will officially complete a reported £75 million switch to Liverpool from Southampton on January 1 - in the type of blockbuster deal Klopp was openly sceptical about when United spent £89.3m to break the world transfer record and re-sign Paul Pogba from Juventus in August last year.
"If you bring one player in for £100m and he gets injured, then it all goes through the chimney," Klopp said at the time. "The day that this is football, I'm not in a job anymore, because the game is about playing together.
"Other clubs can go out and spend more money and collect top players. I want to do it differently. I would even do it differently if I could spend that money."
After the 2-2 draw against Burnley on Boxing Day, Mourinho complained a near £300m investment in players since his arrival at Old Trafford was "not enough" to compete with City, who he observed can "buy full-backs for the price of strikers".
With Liverpool now having matched the figure United spent to recruit striker Romelu Lukaku from Everton in July, the Portuguese was invited to comment once more.
"I think the one to speak about it in a specific way has to be Jurgen," he said. "If I was one of you [a reporter] I would ask him about his comments about one year ago.
"[I am] not speaking specifically about that case because in Liverpool they do what they want to do and I am nobody to comment on what they do.
"The reality is if they think the player is the right player for them and they really want the player, they pay this amount or they don't have the player. That's the way the market is at this time."
Mourinho went on to state modern transfer fees are not a useful barometer when looking at how the stars of today compare with former greats.
"When we compare now the amount of money that certain managers and clubs spend, not even with 10 years but three years ago, it is to compare the impossible. You cannot compare the realities," he added.
"Now you are going to say Virgil van Dijk is the most expensive defender in the history of football.
"Was he better than [Paolo] Maldini, or was he better than [Giuseppe] Bergomi, or was he better than [Rio] Ferdinand? You cannot say that.
"It is just the way the market is. If you pay, obviously you pay a crazy amount of money and if you don't pay you don't have the player.
"So, no criticism at all about what Liverpool did, at all. It's just the way it is."