Seattle Sounders star Ljungberg delighted Campbell back at Arsenal
Ljungberg - who starred alongside Campbell in Wenger's Invincibles - believes the move could turn out to be the best bit of business in this transfer window.
He told the People: "Arsene has a policy not to re-sign players and, on the whole, it's one I agree with.
"With Sol, though, he has got the decision completely correct. It is a decision which has made a major difference for Arsenal's chances of winning silverware this season.
"Has Sol lost a yard or two of pace since I played with him? Probably. We all have. But he can read the game as well as anybody.
"In training, he was like a brick wall. Even though he is not as young as he once was, Arsene is one of the best fitness coaches in the world and will have Sol in great shape."