He is convinced it won't be long before those in the know at Chelsea are kicking themselves for letting the 28-year-old walk away.
Robben said: "I think it was a big mistake of Chelsea's letting Joe go, and I am sure the fans feel the same way. At 28 even with his injuries Joe must still be a £15million-pound player in the current market.
"I am sure Chelsea didn't want to sell him, he has already come out and said there are political reasons behind the move and I am sure we will hear more on that when he is ready.
"I know Joe and the decision would have definitely been a footballing one and not a money one."