The Brazil Under-17s international hit the headlines last year when Los Blancos agreed to hand over the large sum for a player who had yet to make his senior debut.
Vinicius, who was handed his first Flamengo start exactly a year ago to the day, was set to link up with Madrid this summer once reaching the age of 18 to comply with UEFA rules.
With the Campeonato Brasileiro now on a month-long break, the teenage forward was visibly upset as he waved to supporters following his side's 2-0 win over Parana on Sunday.
However, asked after the match if he was saying farewell to the club's fans, Vinicius told reporters: "It's not yet defined [when I will go], but in the next few days it will be and I'll let you know. Flamengo, Real Madrid and my representatives are going to decide.
"Flamengo is the club that always helped me, took me out of Sao Goncalo and gave me a better life, took care of me. I just have to thank everyone who has helped me since I got to Flamengo.
"[Flamengo director of football Carlos] Noval is asking for me to stay a lot, but it is not me who will decide. It's a difficult moment. I'm where I've always dreamed of. I could be saying goodbye to the greatest fans in the world, alongside my family, friends and everyone present.
"I did not expect to make my professional debut so soon and at 17 be able to leave and play for Real Madrid."
Barcelona were also rumoured to be in the running to sign Vinicius, who starred for national side Brazil at the 2017 South American Under-17 championship.