Haaland was a goal machine in 2019/20, banging in 44 goals in 40 appearances for RB Salzburg in the first half of the campaign and then with Dortmund after moving to the Bundesliga in January for a €20m fee - a fee which looks more like a bargain with every passing day.
Despite only being with Dortmund for eight months, rumours have already started about where he could move next, with Manchester United and Real Madrid believed to be leading the pack for a potential transfer.
He is still just 20, and Lagerback reckons that only Messi and Ronaldo made a similar impact on the game at that age.
"I've maybe been around too long but I have never seen a guy since maybe Messi or Ronaldo that developed at such a young age," the Norway boss said.
"That's very unique and he has all the possibilities to become a really world-class player - if you look at the offensive third of the pitch and in the box then he's already absolutely top class.
"He perhaps has a little bit more to do in the link play but being so young, he's already at a really high level.
"With the qualities he already has and his focused personality - if he can stay free from injury then he can be a really top-class player."
The Dortmund striker scored for Norway in the Nations League last week but the Norwegians ultimately succumbed to a 2-1 defeat versus Austria.