Namesake of Celtic's 20-year-old French striker Moussa Dembele—who has been prolific for the Hoops' first team this season following a summer move from Fulham—the 2003-born Dembele replaced Jack Aitchison in the 81st minute against Hearts, per football writer Liam O'Hare:
Per Celtic's match report, "the diminutive playmaker didn’t look out of place and played his part in the closing stages."
According to PA Sport (via ESPN FC), Dembele has recently been named player of the tournament at both the St Kevin's Boys club competition in Dublin and Bassevelde Cup in Belgium—which Celtic won—and he is more regularly a star in the under-14s and under-15s.
The below video shows a glimpse as to what he is capable of, and hints at why he was given his chance in the under-20 side:
As noted by Bleacher Report UK, the Celtic youngster could soon add himself to the string of Dembeles currently pulling up trees across Europe:
Along with Celtic's Moussa, Ousmane Dembele, 19, has started his Borussia Dortmund career brightly following his summer move from Rennes, while Tottenham Hotspur are still awaiting the return of 29-year-old Mousa Dembele from injury.
Given how early Karamoko has made the step up to under-20 action, it may not be long before he joins them at a senior level in European football.