The 20-year-old offers an alternative to Ahmed Elmohamady, Andre Green and Albert Adomah in the wide areas and could also play centrally if required.
The Spurs acadrmy product has made 32 appearances for the London side since making his first-team debut in January 2015 in a FA Cup Third Round replay against Burnley.
The 20-year-old midfielder has made 32 appearances for Spurs, a lot of them as a substitute, and was part of the England team that won the U20 World Cup this summer.
An impressive distributor of the ball, Onomah was successful with 78% of the passes that he attempted in the Premier League last season.
But there's more, and it's important if you are a fan of Joshy: at the same time, the club also announced that Onomah has signed a new contract that will keep him a Tottenham player through 2020-21.
Grealish suffered kidney damage during Villa's pre-season encounter with Watford on Saturday, and is expected to spend at least three-months on the sidelines.
He told Aston Villa's website: "I can't wait to get started".
The Enfield-born midfielder may have designs on breaking into Pochettino's starting line-up in the future but is now exclusively focusing on helping Aston Villa earn promotion back to England's top-flight.
On the other hand, Aston Villa have been rather active in the transfer market this summer and have pilfered a number of players from Premier League sides.