Brentford have missed out in the chase from Besar Halimi after FSV Mainz 05 announced the capture of the midfielder.
The Bees had been interested in the Stuttgarter Kickers attacking midfielder but the 20-year-old opted to stay in Germany.
"He has a very big footballing potential that we continue to develop in the next four years and raise to a higher level will," said FSV manager Christian Heidel.
"We are convinced that he can make the leap into the Bundesliga."
The Bees also added to their swelling midfield ranks by bringing in Chelsea's Josh McEachran in on a four year deal.