Villa are currently 19th in the table with a game in hand over the teams around them, but there is no guarantee that the campaign will be allowed to safely resume in the coming weeks.
Manchester United have reportedly stepped up their interest in the 24-year-old ahead of this summer's transfer window, and Merson has claimed that Villa stand no chance of keeping their captain if they are relegated.
"I would say 100%. If Villa go down then I think they will get rid of Jack and he will be sold," Merson told Sky Sports News. "He's a Villa man through and through, he loves Aston Villa, but he will have to move on, there is no doubt about that if he wants to better himself.
"It's horrible saying that, better yourself, because it's a great club, but he will have to play in the Premier League."
Villa are believed to value Grealish in the region of £70m, although the price could fall to £50m if they drop into the Championship for the 2020-21 campaign.