He said: "The club didn't need to be sold to me because everyone in Europe knows about Nottingham Forest and I saw this as a great opportunity to come and play football for a good club."
Sonner is currently carrying a knock that he picked up in the friendly against Scunthorpe so may well start on the bench.
Sunderland will be looking to bounce straight back to the Premiership but new signing Gary Breen is unlikely to feature against Forest in front of the Sky cameras.
The 29-year-old defender, who was released by West Ham last season, signed a two-year deal with Sunderland but is fighting to get fit following his last match on 11 June.
Manager Mick McCarthy said: "We've had five weeks' training and seven pre-season games – Gary has had none of that. I’ve got to curb the urge to rush him into the side. It would be remiss of me."
Striker Kevin Phillips could also be unavailable for selection if he can complete his £3m switch to Gordon Strachan's Southampton.