It has been reported by Sky Sports that Championship club Forest want to secure the services of the 28-year-old winger on a loan deal.
New Forest manager Chris Hughton worked with the winger when they were at Premier League club Brighton and Hove Albion.
The Frenchman spent the 2019-20 season on loan at Fulham from Brighton and helped the Cottagers cliched promotion to the Premier League via the Championship playoffs.
The former Leicester City winger made 34 starts and 11 substitute appearances in the Championship for the Cottagers last season, scoring three goals and providing four assists in the process.
Fulham signed Knockaet on a permanent contract earlier this summer for 10 million pounds, but the winger has yet to feature in the Premier League for the London club this season.