Kroos completed his move to the Champions League holders last week after starring for World Cup winners Germany this summer.
"Kroos is a great player. I have seen him for many years. He has great quality and I had the opportunity to play against him," Senna told Marca.
"He is a sure star and will triumph in Madrid."
Senna spent 11 years in La Liga with Villarreal before leaving for New York Cosmos in 2013.