Williams first arrived at Brentford in July 2015 before becoming their assistant head coach in September. He arrived in Nottingham last December and now finds himself in caretaker charge at the City Ground.
One Brentford player has now been speaking about meeting his former coach.
“I have a lot of respect for Paul and have a good relationship with him.
“He helped me a lot during his time here and he pushed me a lot while I was playing and I have great respect for him.
“He was a coach at Southampton so we knew he had it in him and I think he’s just stayed in football and his chance has come and he's taken it.”
“At the end of the day he’s going to be an opponent and he’s not on my side anymore so I’ll be looking to win.”
Forest go into the game in need of a win after defeat to local rivals Derby County just before the international break.
Brentford and Yennaris however travel to Nottingham needing a win to potentially move them clear of the relegation zone in the Championship – and move level on points with Forest in the bottom end of the division.
Forest fans will hope that Williams’ inside knowledge will help them take the win.