The German midfielder has been a pivotal player for the capital side, making over 150 appearances since his €25 million move.
Last season, Luis Suarez was the only La Liga star to register more assists (13) than Kroos' 12, and only three created more chances than he did.
The fee Madrid paid for the 27-year-old looks very cheap in comparison to the sums being spent on players three years later, after Neymar made a €222m move to Paris Saint-Germain and Barcelona signed Ousmane Dembele for a price that could reach €147m.
And the World Cup winner has proven to be incredible business for the Spanish side, his agent maintains.
"If you look at the fees today, and remember that Toni moved for €25 million, you can say that he is the bargain of the century for Real," Volker Struth told Sport Bild .
"The Real Madrid board are still happy to have signed a player of such class, as they told us after the Champions League final in Cardiff. Just for comparison, James Rodriguez [now at Bayern] moved to Real Madrid from Monaco for €80m in the same year."
Struth also touched on Dembele's move to Barca, criticising the 20-year-old for forcing a way out of Borussia Dortmund by refusing to train.
"Because of guys like Dembele I have a shitty reputation. It annoys me that people say the agents told him not to come go to the training sessions anymore," he added.
"The agents! So, me too! I'm sick of that. That kind of attitude from a player is a no-go. If one of my players did that, I would immediately part ways with him. Where will it end?
"There is enough lies and nonsense told and written about our job. I wish for more transparency."