The Nigerian international was without a club having left Coventry following a brief and unsuccessful spell with the League One club.
He picked up a hamstring injury late last season and saw his contract mutually terminated after featuring just twice.
Yakubu played for numerous clubs in England, first joining Portsmouth on loan while playing for Israeli club Maccabi Haifa.
Last month, Yakubu was pictured training in the gym with
Yakubu scored 21 goals in his 57 appearances for Nigeria after his debut in 2000, and remains the third highest ever international goalscorer for his country.
3 - Yakubu is one of only three teenagers to have scored a hat-trick in the Champions League (19y 306d for Maccabi Haifa v Olympiakos in 2002), alongside Wayne Rooney & Raúl. Retired. pic.twitter.com/MGbmrOIk2T— OptaJoe (@OptaJoe) November 22, 2017
His most fruitful spell in England's top flight was with Portsmouth, where he scored 28 goals across two seasons at Fratton Park.