The Spanish side have shown the veteran Ghanaian midfielder the exit after failing to shine ahead of the start of the new term
The Ghanaian spent last season with Fulham going through sweltering conditions and had to move to the Spanish side after the Craven Cottage outfit went on relegation.
Vallecano confirmed in an official statement on Monday that the Ghanain midfielder has left through mutual consent and joining top-flight side Eibar.
"Rayo Vallecano de Madrid and Derek Boateng have reached an agreement for the termination of the contract between both parties. The player will play in SD Eibar. From the club we wish him well as the new phase begins," the statement read.
The 31-year-old had difficulties in meeting the standards set by head coach Paco Jemez.