The former Gunners midfielder has impressed in his loan spell at the Hammers, who lie fifth in the table.
Wenger helped mould Song after signing him from French outfit Bastia and is not surprised the 27-year-old has gone onto play for Barcelona.
He said: “I brought him here at the age of 17 and kept him despite all the opinions against him.
???He developed into a very good player, so you don’t need to convince me he is a good player.
“I think he was a very good player when he was here and he didn’t play a lot when he was in Spain – you see players like Santi Cazorla who always looks stronger (when they play regularly).”
Arsenal can leapfrog West Ham with victory and are just two points behind fourth-placed Southampton, but ahead of Tottenham only on goal difference.
With so little between the sides around the Champions League places, Wenger wants his players to concentrate on continuing their fine form which has seen them lose just once in their last eight games.
“I don’t give importance to the table at the moment,” Wenger added.
“There are 20 games to go. It is very tight and it is down to consistency now.
“We know every game now is down to consistency and reproducing the performances.
“We need to prepare quickly, focus quickly and that is an ability we want to show at West Ham.”
Defender Laurent Koscielny could be available for the game at Upton Park following a calf injury, while midfielder Alex Oxlade-Chamberlain faces a fitness test.
With Olivier Giroud suspended for three matches after his red card against Queens Park Rangers, Theo Walcott is expected to return to the attack.