The 19-year-old only joined the Foxes last week in a £3.5m switch from Birmingham City and was thrust straight into the starting line-up for the third round tie at White Hart Lane.
Tottenham Hotspur 2-2 Leicester City
The Emirates FA Cup
Third Round Proper
Sunday 11 January 2016
White Hart Lane, Tottenham Hotspur
Live on BBC 1
And the England Under-20 forward didn’t disappoint, linking up well with Young Lions and new Foxes team-mate Ben Chilwell on the left.
Harry Kane's late equaliser may have spoilt Ranieri's day after Leicester led the game for most of the second half, but he was pleased with Gray’s performance.
"I’m very pleased because it’s not easy," said Ranieri after the game, which will be replayed at the King Power Stadium next week.
"He’s so young and he played for the first time against a Premier League –Tottenham.
"Of course he will improve more, but he’s a very smart boy and will improve a lot.
"But it’s fantastic [to see them play so well together] because they are the future of Leicester."
Both Gray and Chilwell were called into Gareth Southgate’s England Under-21s squad last November, after impressing with the U20s before that.
Emirates FA Cup highlights: Tottenham Hotspur 2-2 Leicester City