Grealish has been heavily linked with a move away from Villa Park in recent weeks, with Manchester United appearing to be the frontrunners for his signature.
However, Dean Smith's side are currently locked in a relegation battle in the Premier League, despite the 24-year-old registering seven goals and six assists in 24 league appearances this term.
Agbonlahor, who netted 86 times for Villa, believes that a move to the European champions would be the best move for the Englishman.
"I am not just saying this as I have played with him, but I honestly think he is the best attacking midfield option that England have got at this current time," Agbonlahor is quoted as saying by the Daily Star.
"That is why, when people say Grealish to Manchester United, he could do so much better than that, and he could walk into any team in the world, even Barcelona or Juventus. For where Manchester United are now, he could go to better teams around the world.
"So he doesn't need to limit himself to just United and focus on teams who are playing in the Champions League. He is the missing piece that a lot of teams need right now. I watch Liverpool, and they are an outstanding team, but they are missing a player like him.
"There are a lot of teams that he would walk into, so it is down to Villa to have the resolve to reject bids and for them to grow as a club because they aren't a team that should be fighting with relegation."