The Foxes take on the Citizens in midweek Premier League action, and the former Manchester United star was asked about the Norway international’s form.
The reporter suggested Haaland was having a bad season, but the manager dismissed the claim about the 24-year-old.
"How many goals did he score so far this season? Yesterday he scored his 30th. Come on. This is what I mean? 30 goals - he's the best striker in the league, " Nistelrooy told the media.
"He's proven it. He's won everything possible. He's a class act. He's the best of the best. He has an A mindset, A quality and will continue with that for many more years.
"He has signed an extremely long contract and is one City is building around. When you have a guy like that in the building and you're keeping him, you have a guarantee for 30 goals and apparently it's a bad season. Imagine when he starts to play well - he'll score 60 or 70! He's a pillar in City's current team and in their future, so nothing but praise for him from my side."
Before his ankle injury setback, Haaland has scored 30 goals in 40 games in all competitions for Pep Guardiola’s men.