Arsenal Supporters' Trust (AST) have urged Alisher Usmanov to turn down Stan Kroenke's offer of £525m for his 30% stake in the club.
The Guardian have reported that Kroenke Sports Enterprise UK have attempted to secure the 18,695 shares held by Usmanov's Red and White Securities Limited.
If Kroenke were to complete the purchase of Usmanov's stake, he would increase his shareholding to over 97%.
Usmanov has repeatedly stated that he will not sell his share in the club, but he has not been given a place on the board.
The Russian businessman has previously made a £1bn, which was responded to with a statement from KSE in May 2017 claiming that the "shares are not, and never have been, for sale".
AST are believed to have made contact with Usmanov's representatives after reports he could now be willing to sell.
If Kroenke was to successfully obtain Usmanov's share, there will be concerns over the possibility of Arsenal becoming a privately-owned company.
A policy statement, published on the AST website in 2016, said: "The AST continues to believe that Arsenal is too important to be owned by any one person.
"The best ownership model for Arsenal will always include supporters being represented and involved in the ownership structure as shareholders.
"We understand the reality that any stake in Arsenal is available to buy at any time should someone make an acceptable bid, but we will oppose any attempt to buy the club outright and take it into single ownership."