Vieira told the Sunday Mirror of Gallas: “He is a positive person and he can play in a number of positions – at fullback or in central defence.
“Some people laughed when he left Chelsea to go to Arsenal, but you only have to look how well they are doing now.
“William has made a big contribution to that. He will have had a great influence on the younger players with the advice he has given them.
“He is a great character to have around the club – and a very important player for Arsene Wenger.
“He never gives up and will bring the best out in the young players around him. I have played against him and he is a very difficult opponent. I’ve played with him for France and he is a great player to have on your side. He has great experience and Arsenal will need that in the second half of the season.
“William has been a great signing for them. He is also happy there, you can see that.”
