Boateng's Middlesbrough deal runs out in June

Boateng's is out of contract at the end of June and the club are eager to keep hold of the 29-year-old.

Agent Barry Silkman, who claims he had been brokering a contract, says both parties were close to cutting a deal.

But Middlesbrough refused to comment insisting that Mr Silkman was "no longer involved with negotiations".

Silkman claims he had been negotiating for Boateng on behalf of the player's long-term agent Sigi Lens, who runs the Fifa-registered Pro-Athlete Sports Management agency in Holland.

But Silkman told BBC Sport: "We had a disagreement and I'm no longer involved in the deal.

"I don't know what will happen now as I'm not negotiating on behalf of George anymore.

"It's a very difficult situation but these things happen in football sometimes."

Lens was unavailable for comment.

Boateng, who joined Boro from Aston Villa for £6.5m four years ago, has been a key figure in the club's march to the semi-finals of both the FA Cup and Uefa Cup this season.

He was again instrumental in Wednesday's 4-2 FA Cup quarter-final replay triumph over Charlton at The Riverside.

And his team-mate Mark Viduka is urging the club to tie up new deals for Boateng and another Dutchman - striker Jimmy Floyd Hasselbaink - or risk the break-up of a side on course for glory.

It would be a great loss if Jimmy left Boro, and the same goes for George. Mark Viduka

Hasselbaink, 33, is also out of contract at the end of the season and Aussie star Viduka said: "I'd definitely love to continue my partnership with Jimmy into next season.

"I enjoy playing alongside Jimmy, he is a great player, a great member of the squad and a good person to have in the dressing room.

"He is very positive, a born leader, and those sort of people you need in teams, while his finishing is second to none.

"He is a very dangerous player to have in the team, and it would be a great loss if Jimmy left Boro, and the same goes for George.

"We want to keep hold of all our best players because this team I hope is on the verge of great things."