The 22-year-old had agreed personal terms with the club and all that was left was for the Italian side to agree a fee with Marseille.
However, according to Sky Sport Italia, AC Milan are hopeful of beating Inter to the signing of Imbula and have made a late bid for his services.
The bid reportedly made by the Rossoneri is allegedly worth £20 million for Imbula, who is yet to make an appearance for the France national team. However, the current Marseille midfielder is eligible to play for three countries having been born in Belgium, as the son of Congolese parents and growing up in France.
In 2013, when Imbula played for En Avant de Guingamp, he was voted best player in Ligue 2. He joined Marseille later that year.
Marseille finished their 2014/15 Ligue 1 campaign in fourth place, meaning that they missed out on qualification for the Champions League.