Leicester go to Liverpool later today on Boxing Day. Slot faced Foxes manager Van Nistelrooy when the pair were competing in Eredivisie.
“I think the positive (for Leicester) is that teams that are positioned in the lower side of the league table, they mostly lose games, but since Ruud (van Nistelrooy) is there they also won a few,” he told reporters during his pre-match press conference.
“So that shows you that he has done really well, especially when he came in. Now I think he had two tough results in a row. These teams, all of them, it is special for them to go to Anfield and they know if they go to Anfield they have to be at their best, so they will never underestimate us.
“And hopefully maybe that’s the good thing about these 15 minutes we saw (on Sunday), that we understand we cannot underestimate one minute in the Premier League because then we are not as good as we might think we are if we are on top of our game.”
On Van Nistelrooy's demise at PSV, former Feyenoord coach Slot also said: “I was expecting you to tell the people over here that I lost once and drew once, but you made it positive saying that we won the league title! Which was true.
“Cody Gakpo was in his team, so I am happy he is in my team now when we face Ruud, because I think in both games he scored.
“Ruud is a very nice person, first of all. I’ve met him once or twice. And I think he did really well when he was at PSV because for the last one-and-a-half years they have been on top of the league table, but if you look at the second half of Ruud’s season I think they didn’t even lose anymore, at all.
“So it wasn’t a surprise that after he left and they bought so many players – because PSV started buying a few more players than they did when he was working there, because when he was there Cody Gakpo and (Noni) Madueke were sold.
“But he still showed that he could compete for the title. Nice person, good manager, did well at (Manchester) United as well. Looking forward to seeing him, especially if we win!”