After seven years with Chelsea, which has seen him win five major trophies, Willian is set to leave Stamford Bridge in the coming days.
The Brazilian had wanted a three-year deal to stay but the Blues hierarchy have so far only offered two.
That has allowed London rivals Arsenal to make a move for the attacker and with his agent Kia Joorabchian having close ties with the Gunners, an agreement is likely to be reached.
And Rudiger says Willian's departure would be a sizeable loss to the team.
Antonio Rudiger is a big fan of Willian (Image: GETTY)
He said: “Since day one of coming to Chelsea, he and David Luiz got me into the team and helped me out in the first couple of months because it was not that easy.
“He is a great guy and a really, really good footballer. He is calm and humble and it will be sad if I don’t see him again as a teammate. He is not the type of player who talks that much.
“He does his thing on the pitch, just like Eden Hazard. By playing, he shows what he is about.
“He is a guy who dictates the game and not many players in the world have this type of quality.
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"I’ll be clear, this arrival is an additional motivation," he said. "And I think it was inevitable that the club would recruit a striker.
"Chelsea are a big club, spending money to strengthen the squad, and I was expecting someone to come in.
"With [Hakim] Ziyech and Werner, we will try to be more competitive for next season.
"I am not naive – Werner did not arrive to sit on the bench. I will do everything to ensure that the manager finds himself in a situation when he has to make a difficult choice every week [of who starts]."
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