McKenna, 23, handed in a transfer request last August, with Aberdeen rejecting approaches from several clubs.
The Scotland international is keen to further his career in England and was also the subject of a hefty £7m bid from Aston Villa in 2018, which Aberdeen knocked back.
However, the COVID lay-off has dented Aberdeen’s finances, meaning the club are now not in a position to reject a big offer.
"It has gained a bit of momentum over the last 24 hours," Dons manager Derek McInnes told Radio Scotland when asked about the potential deal.
The Dons said on Twitter: "Aberdeen manager Derek McInnes confirmed on RedTV that the club has received a significant offer for Scott McKenna.
"This is now being dealt with by the Chairman and the relevant club."
Nottingham Forest are thought to be the club in to sign McKenna, with the Reds beaten 2-0 by Cardiff City yesterday.
Sabri Lamouchi’s men are yet to score a goal during 2020/21 campaign.
Defensive duo Joe Worrall and Tobias Figueiredo Lamouch’s first-choice centre-backs but it would seem the Frenchman is keen to add depth to his squad.
McKenna has amassed 16 caps for his country.