Blues boss Roberto Martinez is said to have contacted Stamford Bridge on transfer deadline day to enquire about the Senegalese star's availability, only to be offered the Belgian instead.
"It only came up about three o'clock on the final day. Fortunately, everybody was able to push it through in a hurry," a purported source close to Martinez told The Mirror.
Everton were previously linked with Ba back when he was a West Ham United player, missing out on his signature to Newcastle United.
Lukaku has scored eight times in 12 appearances for Everton this term, and has hinted that he could remain at the club beyond his season-long loan.