The Hammers kept pace with the Champions League chasers until Christmas, but their form in 2015 has seen them slide down the table.
It is a decline that Song believes was always likely to happen, as the Barcelona loanee believes there is a lack of quality in reserve at Upton Park.
"I think we have to target an eighth-placed finish this season," he said. "The problem with West Ham is that we don't have a very big squad. I was saying to people it was too early to say that we will finish fourth or fifth.
"I always said if we finish tenth it would be perfect because we don't have a squad like an Arsenal or Chelsea. When we have one or two players injured, we don't have a big player to come on."
Despite Song's realistic appraisal of West Ham's season, there is still a great deal of frustration being felt around the Boleyn Ground.
The Hammers had raised expectations with their impressive opening to the campaign and their dip in form has been more dramatic than many could have predicted.
West Ham went from looking like one of the most threatening sides in the Premier League to a team who have looked well short of quality, and they have now won just two of their last 16 top-flight matches.
That run has led to manager Sam Allardyce's future being called into question, with the experienced boss's contract expiring in the summer, and it is still not known whether he will be in charge at the start of next season.