After being moved from full back to inside-left, the Aberdeen youngster showed a precocious talent, and was soon selected for Scotland schoolboys. In 1955, the teenager was snapped up by Huddersfield Town, making his debut on Christmas Eve 1956 aged only 16 in a 2-1 win over Notts County.
In October 1958, just before his 19thbirthday, he became one of the youngest players to appear for Scotland, scoring the second of three goals in a 3-0 win over Wales in the British Home Championship.
Two years later, Denis set a new British transfer record when he moved to Manchester City for £55,000. Within a year, Italian club Torino had doubled that fee and set a new record for a transfer involving a British player.