The former England centre-back left Arsenal for Portsmouth in 2006 after scoring in the Champions League final defeat by Barcelona.
Campbell had moved across North London from Tottenham Hotspur in 2001 on a free transfer and was at Arsenal for five years in which they won two league titles and three FA Cups including the double in 2002.
"I didn't imagine he would play as many games as he has (since his return)," Wenger told reporters on Tuesday.
"I thought he would play in one or two games maybe but he got those extra matches because he played well.
"Sol has been a big support for me and the squad. He is very important in the dressing room because he is highly focused and highly motivated," he added of the former Spurs captain.
"I must say, every time he has played he has turned in a very good performance," added Wenger. "It's one of the good signings I've made. I've no concerns about him. I can tell you he'll play tomorrow."
"I could never see him going back to Arsenal in a million years," he said. "When I took him he wanted out and they wanted him out as well. He walked out on a fortune at Arsenal.
"It cost him millions and millions. He was losing about 3 million pounds a year (leaving Arsenal) but he just felt he didn't want to be there."
"It was a great lift for him to go back to Arsenal," said Redknapp. "For Arsenal to take him back was amazing."
"I can't think of anyone who gets much worse (treatment) than him (in England)," he said. "They're not going to forgive him, the fans."
