Grealish has received his first Under-21 call-up since opting to play for England and not for the Republic of Ireland.
The 20-year-old Villa man, who can play as a winger or as an attacking midfielder, has been named in Gareth Southgate’s 20-man squad for the Toulon Tournament.
Gardner, who was on loan at Championship side Nottingham Forest for the second half of the 2015-16 campaign, has congratulated fellow Villa player on receiving the England Under-21 international call-up.
Grealish has scored one goal and created 12 chances in 15 Premier League appearances for Villa this season.
The youngster has a pass accuracy of 86% and a shot accuracy of 50%, and has won one header, 22 dribbles and five tackles.
Villa have already been relegated from the Premier League and will feature in the Championship next season.