Musa was strongly linked with a move to top-flight champions Leicester, but they refused to meet the £22.8 million release clause in his contract.
Foxes boss Claudio Ranieri is still said to be keen on striking a deal but now faces stiff competition from Southampton, who are seeking a replacement for Sadio Mane after he joined Liverpool.
West Ham were the other English team credited with an interest in the CSKA Moscow forward, but Harris claims it's pure speculation.
"We are negotiating, but I cannot yet name the clubs interested in the player," Harris told RIA Novosti.
"Let me just say one thing: the negotiations have been positive. A move will be agreed soon. We're finalising talks with a Premier League club, but it's not West Ham.
"I was frankly surprised by this rumour. Yes, he's coming to England, but Musa's not joining West Ham."