The 34-year-old's agent, Shep Messing, has warned the Teessiders the player will look to further his career elsewhere if they do not come up with a better deal.

Schwarzer, who is in the final year of his contract, warned yesterday he would have no qualms about walking away from the Riverside Stadium after criticising the club over compatriot Mark Viduka's departure.

Now Messing has revealed his client has turned down Boro's current offer, and while he is keen to stay on Teesside, he will look elsewhere if he has to.

Messing said: "Middlesbrough asked what Mark wanted and we confirmed his wish to remain at the club.

"We put forward a sensible and fair proposition for both player and club.

"We have received a proposal from the club and at this point, we have been unable to agree on terms.

"He has spent over a decade at Boro and loyalty like that is very rare in football today.

"Mark is one of the best and most experienced goalkeepers in the world today.

"He is on top of his game and enjoying the game more than ever. Wherever he plays, Mark has many more great years ahead of him."

Schwarzer, who is currently on Asian Cup duty, joined Boro in a £1.5million switch from Bradford in February 1997, barely three months after arriving at Valley Parade in a £350,000 move from German club Kaiserslautern.

He has made 407 appearances for the club, and was a key figure in both their 2004 Carling Cup triumph and their first qualification for Europe via the league, when his late penalty save at Manchester City handed the Teessiders their highest Barclays Premier League finish - seventh - the following season.

The former Sydney Marconi player signed a three-year extension in January 2005 after withdrawing a transfer request, but has recently been linked with Bayern Munich.

Viduka's departure after his contract was allowed to run down to hand Newcastle the chance to prise him away on a free transfer came as a huge disappointment to both Schwarzer and Boro.

Manager Gareth Southgate has admitted that with hindsight, negotiations with the striker could have started earlier.

The club are not making the same mistake with their first-choice keeper and negotiations are already under way.

Chief executive Keith Lamb insisted yesterday that talks are ongoing, although Schwarzer's outburst did not go down well at the Riverside.

The two parties are currently some distance apart, and while negotiations will continue, the prospect of the club's longest-serving player seeking a new challenge is a very real one.

Messing said: "Middlesbrough and Keith Lamb have been extremely professional with regard to our discussions about Mark's future.

"While I certainly respect whatever their final decision may be, our job is to provide advice and guidance to a man and goalkeeper who we believe is among the best in the world of football.

"If that means parting ways, Mark will always have great memories of his time there."

Schwarzer will be able to talk to interested parties in January and leave on a free transfer at the end of next season should Boro fail either to tie him to a new deal or sell him before then.