IN THE rest of the country, the arrival of swallows is supposed to herald the start of summer. Yesterday, on Teesside, there was a rather more reliable indicator of the changing of the seasons - Bolo Zenden threatened to walk out on Middlesbrough.

A year after first claiming the club were failing to meet his demands, the Dutch midfielder has dismissed the latest attempts to tie him to a long-term deal.

He will be a free agent next month and, while Steve McClaren has spelled out his determination to keep him at the Riverside, Zenden has warned the Boro boss that he must make a radically improved offer if he wants to avoid losing one of his main assets.

"We are still a long way apart," revealed the 28-year-old, who was one of Boro's most improved performers last season. "The ball is in Middlesbrough's court.

"If they want to keep me, they must come back with a proposal that is suitable to me. I have played 49 of the 51 games and the fans made me player of the year, but the appreciation has not been translated into the contract proposal."

Zenden, who is represented in contract negotiations by his father Pierre, issued an almost identical warning 12 months ago.

Months of wrangling ended in the midfielder putting pen to paper on a one-year deal that always looked like providing little more than a temporary fudge.

It looks even more like that now and, after starting his summer with a bang by signing Nigerian international Aiyegbeni Yakubu on Monday, McClaren will not relish more delicate discussions over Zenden's future.

The former Chelsea star started last season on the left of midfield but, after Gaizka Mendieta was ruled out of the rest of the campaign in late October, he switched to a central position that he quickly made his own.

His eight-goal haul was a major factor in making Boro's maiden UEFA Cup campaign a success and he also played a pivotal role in the club's dramatic qualification for next season's competition.

McClaren will be loath to see him leave as he has repeatedly talked of how important both Zenden and George Boateng, who will also be involved in contract talks this month, are to Boro's continued development.

But McClaren will not want Zenden's bargaining to overshadow the rest of his summer plans. The England number two has been monitoring a number of midfielders in recent months and will not be held to ransom over the Dutchman's demands.

A number of foreign clubs are ready to make a move, with Turkish side Fenerbache, who were in contact with Zenden last summer, leading a pack that also includes the midfielder's former club PSV Eindhoven and German side Stuttgart.

"I cannot wait forever for Middlesbrough," warned Zenden. "I will have to compare the other offers."