Collins - capped 58 times - has told his former Hibs striker he will live to regret not playing for Scotland.
He said: "I'd tell Steven to pick up the phone right now and tell the manager he wants to come back and play for his country.
"Football is a short career. He's at his peak just now, scoring goals, and that's when you want to be playing for Scotland.
"Steven or his agent should make the call. Will he regret it if he doesn't? Of course - 100 per cent."