The 19-year-old impressed during pre-season with Roberto Martinez's first team, scoring a screamer in the 3-1 defeat against SC Paderborn 07 in Germany back in August.
Long has gone from strength to strength and made his senior debut as a substitute in the Europa League defeat to FK Krasnodar in December.
He said: "It’s an important period and Chris is ready for that role. I always felt that when Chris joined the first team in pre-season he had something special.
"He has that knack of making the right room and making the right decision and he can score goals out of nothing. That’s a strong quality. I think Chris will be able to show what he can do."