Ferdinand was skeptical about United signing the Nigerian on loan from Shanghai Shenhua in January.
But Ighalo has come in and scored goals, netting in the Europa League and FA Cup already.
His brace helped United to a 3-0 win over Derby County on Thursday.
Ferdinand told BT Sport: "People and myself included were probably thinking Odion Ighalo, where does he fit into all of this?
"If you have an opportunity to sign a player at the beginning of the January window, he is not the guy you are going to sign.
"But what he does bring is a point. A point where they can focus and play into him from the midfield. He offers the platform to run off.