The Hammers boss is hoping he can replicate his form from his first six months at Upton Park this season.
The Barcelona midfielder was a big hit at the Boleyn Ground last season during a season-long loan spell, becoming a key player in former manager Sam Allardyce’s midfield.
He is now expected to complete a permanent move to the club before the transfer window closes and Bilic says he can be a crucial player for West Ham - on the condition that he reproduces the form shown during his first six months at Upton Park, not his very disappointing second half of the campaign.
"He has got a record. He was an Arsenal player and a Barcelona player and all that and we would like to get him," Bilic told reporters, as quoted by whufc.com.
"I think that everybody agrees, West Ham fans, non-West Ham fans and football people from across the country, that especially in the first six months he was exceptional. If we can get him in that stage or type of playing and try to do it for a bit longer over the whole season, it would be crucial for us."
Vital experience and less pressure on Reece Oxford
It is easy to see why Bilic thinks a La Liga winning midfielder can prove crucial for West Ham.
More than anything, Song will add some much-needed Premier League know-how to the side, with the likes of Angelo Ogbonna, Pedro Obiang and Dimitri Payet all new to the division and still learning.
Additionally, it also gives them a more experienced defensive midfielder than youngster Reece Oxford, who, despite his impressive displays so far and obvious bright future, is not an ideal solution for the role long term.