Arsene Wenger's legacy is at risk if he does not receive proper support from Arsenal after signing a new deal, says Alisher Usmanov.
The manager has agreed a new two-year deal to remain at the club, which was announced on Wednesday, ending months of speculation over his future.
Wenger's position came under intense scrutiny after the club missed out on Champions League qualification, although they did win their third FA Cup in four years.
Billionaire Usmanov owns 30 per cent of Arsenal and recently failed in an attempt to buy out majority owner Stan Kroenke.
He urged Kroenke and the club's board, of which he is not a member, to give Wenger full backing to allow the Frenchman to secure a positive legacy at the club after almost 21 years in charge.
"I am pleased Arsene Wenger will continue to manage Arsenal for the next two years - he is one of the best coaches in Europe," Usmanov said in a statement.
"What is now of paramount importance is that he receives the full support of the board and the majority shareholder.
"He has a great opportunity to deliver the success that the fans deserve and the legacy his long contribution merits.
"However, without the right support there remains a real risk his legacy will be tarnished.
"If the support is not forthcoming we stand ready to step in and do everything we can to deliver success on and off the field."