While the 27-year-old is yet to be officially unveiled as a Bayern player, the transfer is expected to go through in the coming days, bringing an end to his disappointing spell in La Liga.
In his final full season at Anfield, the midfielder registered 14 goals and nine assists for the Reds in all competitions.
And Grujic, who played with Coutinho at Liverpool and is currently on loan at German side Hertha Berlin, believes the new addition at Bayern will add an extra level of skill to an already talented squad.
“He is a special and exciting player, he does crazy things. He got incredible tricks and skills in his locker. I enjoyed every training session with him in Liverpool. He will be by far the best footballer in Germany.”
Coutinho’s signing is Bayern’s sixth new arrival of the summer following Benjamin Pavard, Lucas Hernandez, Jann-Fiete Arp, Ivan Perisic and Mickael Cuisance, who joined the club in the off-season.
However, despite a busy summer of transfers, Bayern did not start the new season with a win, as the Bavarians were held to a 2-2 draw by Hertha on Friday night.
Grujic was one of the visitors' goal scorers at the Allianz Arena, while Robert Lewandowski netted two for Bayern.
“I don't think he'll need that much time to adapt to our system and ideas,” Lewandowski claimed. “"I think he's the sort of player that can settle in without many problems.”