Viduka's 19 goals for the Teessiders last season were vital as they dragged themselves away from the relegation dogfight.
Gareth Southgate: "He is an outstanding player. He was terrific for us, especially at the end of last season. He was a huge player for us.
Boro Gunning For Viduka!
"I have spoken to him since his move, as I did when he let me know he was going, and I was as manager very grateful for what he did for us.
"He was excellent as a player for me last year and as a character, I enjoyed working with him and I wish him all the best.
"But, as he knows full well, he will get nothing but a hard time on Sunday.
"Yes, we have lost a couple of players, but we have added several good players to our team, some of whom have not even had the opportunity to play for us yet this season, and we are looking forward to that challenge.
"You have to be a club that can deal with difficulties, deal with setbacks, but there is not a player in the world who goes out and wins a game on his own.
"You have got to deal with people leaving. Everybody in every walk of life has been replaced at some time or other.
"It might take a little while, I have no idea, it might have an adverse effect on the team for a while.
"But we are determined to work through it. We know where we want to take this club, and we will work towards that.
"If people do not want to be part of that, it is pointless trying to drag them along with us.
"It's better to say 'we wish you good luck', and then we move."