Arsene Wenger has not been surprised by the impact former Arsenal midfielder Alex Song has made at West Ham this season.
Song spent seven seasons at Arsenal under Wenger before leaving for Barcelona in 2012.
The Cameroon international then returned to the Premier League with West Ham in August, agreeing a season-long loan, and has quickly established himself as a key figure for Sam Allardyce's fifth-placed side.
Song will face his former club on Sunday when Arsenal visit Upton Park and Wenger has spoken of his admiration for the 27-year-old.
"He's a good player, Alex Song. I brought him here at the age of 17 and kept him despite all the opinions against him," said the Arsenal manager.
"He developed into a very good player, so you don't need to convince me he's a good player. I took him at a very young age and gave him his chance.
"I think he was a very good player when he was here. He didn't play a lot in Spain but you can always improve for as long as you play. You see players like Santi Cazorla, they always look stronger. When you want you can always improve."
Arsenal beat QPR 2-1 on Friday to move within a point of West Ham and Wenger is now hoping to build momentum during a busy period.
"We have 20 games to go. It's very tight, it's down to consistency now," he added.
"We know every game now is down to consistency. Christmas is a bit special in England because you have to recover quickly, prepare quickly, focus quickly - and that is an ability we want to show at West Ham."