Robert Says "Sorry"
He is currently on a year long loan contract, and it was hoped that Pompey would make the deal permanent, but obviously that is looking very unlikely now.
Pompey boss Alain Perrin could only name four players on the bench at the Stadium of Light after his fellow Frenchman ruled himself out, apparently citing injury.
Portsmouth chairman Milan Mandaric demanded an explanation or apology.
"I am very sorry for the team, players and the manager for any misunderstanding," Robert told Sky Sports News. "My hamstring was very sore after training on Friday. I travelled to Sunderland but became confused because Salif Diao got injured on Saturday morning.
"I wasn't 100% to play or sit on the bench. I know my body and prefer to rest. I told the manager and he understood. I am very sorry for any confusion."