The 27-year-old was at Bayern Munich when he was attracting interest from the Red Devils. Their former manager David Moyes had earlier confirmed he was keen on bringing him to Old Trafford from the Allianz Arena in the summer of 2014.
United sacked Moyes just 10 months into his six-year contract in April 2014 and was replaced by Louis van Gaal. The Dutchman's arrival forced Kroos to reject the 20-time English champions, which then allowed Real to secure his services.
Kroos admitted that his decision to change the team was "correct" and also heaped praise on Real manager Zinedine Zidane for improving him as a player.
"My change of team was correct, in fact, from my point of view there is no doubt about it. Clearly, if you go abroad to a top club, it means one more step in your development. Carlo Ancelotti wanted me in Madrid, and had bet on me," Kroos was quoted as saying by the Mirror.
"From the beginning, he (Zidane) gave me a lot of confidence. And in his two years he's played me in almost every game, especially in the big games.
"Trust me, I will always try to give everything for the team. We have a good relationship. A friendly relationship with the coach is important for each player."
Since joining the Spanish capital club, Kroos has won the Champions League, Uefa Super Cup and the Fifa Club World Cup on two occasions. Besides, he has added the La Liga medal to the list of honours. Kroos signed a new contract at Real in October 2016 and his current deal will keep him at the he Santiago Bernabeu until 2022.