Sheffield United transfer news: The chain of events which could see Blades lose Sander Berge but gain Lewis O'Brien

It emerged at the weekend the Blades are open to selling Norway international Sander Berge, having dug their heels in to keep him during the last transfer window.

But the picture has now changed, with the club under a transfer embargo for failing to pay an instalment on a transfer fee, and in talks over a possible takeover.

Manager Paul Heckingbottom is keen to sign a forward to replace Reda Khadra – whose loan was cut short by Brighton and Hove Albion earlier in the window – but they can only register new players once the debt is settled.

The embargo will be lifted immediately the unpaid money is lodged with the Football League but failure to settle the matter this week could lead to further sanctions. In over a week since the news emerged, the Bramall Lane club have been unwilling or unable to clear their debt any other way.

Berge was withdrawn from his side’s FA Cup fourth-round tie at Wrexham so as not to risk an injury which could jeopardise a move. Heckingbottom was told of the decision just before Berge was due to board the team bus on Saturday.

Without him, the Blades were held to a 3-3 draw by Conference side Wrexham and must now win a home replay next week if they are to host a lucrative fifth-round game against Tottenham Hotspur.

Heckingbottom has made it plain he does not want Berge to be sold with his side well placed to win promotion to the Premier League but has been just as forthright in saying it would be "foolish" to do so without signing a replacement before Tuesday's 11pm deadline.

He also revealed he has provided the club with a list of players he wants to sign should Berge go. O’Brien is thought to be on it.

Fulham emerged as the initial front-runners but are close to signing fellow midfielder Sasa Lukic of Torino, and it is unclear how this will impact their interest.

Napoli, Brighton and Hove Albion and Newcastle United have also been linked.

Brighton have told holding midfielder Moises Caicedo to stay away from the club until after Tuesday's 11pm deadline with a move to Arsenal a growing possibility, particularly now Chelsea look set to sign Enzo Fernandez for a British transfer record fee of £105.6m instead.

Newcastle are also said to be interested, and them signing Berge could kick off a sequence of events which frees up O'Brien.

Newcastle midfielder Jonjo Shelvey is expected to join Nottingham Forest, which would allow O'Brien to leave after an underwhelming summer transfer.

One of the star players in last season's Championship, Huddersfield academy graduate O'Brien has only made six Premier League starts this season, five in August.

Complicating matters was Newcastle manager Eddie Howe's assertion on Monday that "permanent signings will be difficult" given the constraints of financial fair play rules on a club which has spent big since being bought by Saudi Arabia's Public Investment Fund last season.