Usmanov, joint owner of the company Red and White that bought former vice-chairman Dein's 14.58% holding in the club, called Arsene Wenger "the best manager in England" but insisted he viewed the shares as an investment.
Dein, who was forced out of Arsenal in May, has been made chairman of Red and White and given the task of acquiring more shares.
Usmanov said in the Evening Standard: "I have been an Arsenal fan for eight years and I think the club has the best manager in the Premier League.
"But this purchase of mine is not a strategic or political one. It's a portfolio investment.
"Arsenal as a business is undervalued. My aim is to steadily increase my package because I think the value of it will grow and will soon reach a higher level. The club has everything to achieve it."