The Portugal U21s international, who can play on the wing or as a striker, replaced Bryan Ruiz in the 69th minute to aid his side's 2-0 victory over Feirense.
Leao has a rather impressive goal tally, having scored six goals in 11 matches for Sporting.
Whilst still just a rising star, scouts at City will be hoping they can land Leao sooner rather than later before increasing interest causes his pricetag to inflate.
In the mean time, the Portuguese teenager is certainly a player to keep your eyes on.