Celtic helped his asylum-seeking family stay in Glasgow after fleeing Somalia in 2001 when the late Tommy Burns — then head of youth — lobbied government officials.
Feruz made his first senior outing in Burns' memorial game in 2009.
Rui Alvez said: "Islam would love to thank Celtic for all they did for him and his parents.
"We appreciate everything Celtic and Tommy Burns did for him.
"Neil Lennon is a friend who I deeply admire but it was in Islam's heart to move to Chelsea. He's the one serious player in Scotland. He is Scottish and will one day score goals for Scotland."