Future of Mauricio Pochettino thrown into doubt as Southampton chairman Nicola Cortese resigns

Cortese was understood to be at loggerheads with club owner Katharina Liebherr over the demands of running the club that have significantly increased since their Premier League return

The prospect of Mauricio Pochettino staying on as Southampton manager is in doubt after executive chairman Nicola Cortese's departure was confirmed.

On a day of politics and confusion at St Mary's, a statement released by the club at 7pm brought an end to the Italian banker's reign after more than four years at the helm.

A collapse in Cortese's relationship with owner Katharina Liebherr – who will now become non-executive chairman for the South Coast club – is believed to be the main reason for his resignation after rumours of disagreements between the pair emerged late on Tuesday night.

"With great regret we have accepted the resignation of Mr Cortese," read a club statement. "He has done a wonderful job at the club and we very much wanted him to stay."

With Pochettino known to be a major ally of the departed chairman, the club may soon be looking for a new manager too. Cortese has not always been loved by the fans – not least because of the change in kit colours from red-and-white stripes to plain red – but he was close to Pochettino.

Cortese made the controversial decision to replace Nigel Adkins, who guided them to promotion in 2012, with Pochettino in January last year but since then Southampton have improved and sit in ninth place in the Premier League.

When asked about Cortese's position last year, Pochettino was clear how supportive he was of the Italian, raising questions over his future should Cortese leave.

"I would not understand a Southampton without Nicola being here," Pochettino said. "The person who actually called me from the start, told me about the project and put his faith in me, in this club and as a manager was Nicola. Nicola Cortese has basically been the reality at Southampton for the past four years."

In 2009 Cortese conducted the deal to buy Southampton from the administrators on behalf on Swiss businessman Markus Liebherr. His death in 2010 led to his daughter Katharina taking a more active role. Cortese almost left at the end of last season after reportedly falling out with her.

It was suggested that Manchester United would test the club's resolve by putting in bids for England midfielder Adam Lallana and highly rated left-back Luke Shaw – who tweeted he was "gutted" at the news – while West Ham could put in a second bid for striker Rickie Lambert.