The Wolfsburg defender believes that the striker is amongst the very best in the world, a sentiment shared by Polish legend Zbigniew Boniek, who feels that he would suit Barcelona
The Poland international will be expected to lead the attack for BVB against Bayern Munich, who have earned the tag of favourites due to their domination in the Bundesliga where they finished 25 points above the Schwarzgelben.
However, Lewandowski outscored every other Bayern attacker in the league this season and is just two goals away from sharing the European tournament's golden boot for this campaign with Cristiano Ronaldo, a feat that Kjaer would not begrudge the Pole.
The centre-back told Ekstra Bladet: "Lewandowski is a complete forward and has impressed me when I have played against him.
"We did win in Dortmund [3-2 in December] but, on that occasion, he did show me that he has the potential to be a world-class striker."
Polish legend Zbigniew Boniek lavished even more praise on Lewandowski, who is believed to be keen to leave Signal Iduna Park this summer, suggesting that Liga champions Barcelona would be an excellent fit for the striker.
"Robert Lewandowski is a player for Barcelona, he has plenty of quality and character to play alongside those monsters such as [Lionel] Messi, Xavi and [Andres] Iniesta," the current chairman of the Polish Football Association told reporters.
"Besides being able to score goals, he has the nose of a goalscorer, I assure you."