An investment firm co-owned by billionaire Alisher Usmanov have increased their stake in Arsenal to 25 per cent.
Red and White Holdings first invested in Arsenal two years ago when they bought the 14.65 per cent holding of former vice-chairman David Dein.
The company owned around 24 per cent before making their latest move, which was confirmed in a statement from Arsenal Holdings PLC today.
If the stake was to reach 30 per cent, the company could launch a formal takeover bid.
Arsenal's board of directors have remained steadfast in their determination not to sell out for some time.
Their "lockdown" agreement means no director can sell their holding before April and thereafter must give each other first option.
The situation changed in December, however, when Lady Nina Bracewell-Smith was forced off the board, and her 15.9 per cent holding was consequently freed from the agreement.
A further 12.4 per cent is owned by American businessman Stan Kroenke but he has aligned himself with the directors having accepted a seat on the board.
The other major shareholder is Daniel Fiszman, who owns a 24.11 per cent stake.
Usmanov is a Russian oligarch of Uzbek origins with a fortune of an estimated USD4.5billion.
A statement from Red and White Holdings confirmed the company now held a stake "in excess of 25 per cent" in Arsenal.
It continued: "We are pleased to have now secured over a quarter of the shares of Arsenal.
"We are committed long-term investors and supporters of the club and are comfortable that we are now in a protected position.
"We also welcome the strengthening of the squad and look forward to a successful conclusion to the season."