NEWCASTLE United's fears over the future of Alan Shearer have been underlined by an audacious approach for Barcelona's superstar striker Patrick Kluivert.

Skipper Shearer, who underwent a make-or-break operation in May to cure niggling tendinitis in his left knee, is not expected to return to action until late September at the earliest.

The surgery, carried out by world-renowed knee specialist Richard Steadman at his Colorado clinic, was declared a success and Shearer is now almost halfway through a four-month rehabilitation programme.

But United are privately worried that the former England captain may not regain full fitness and that if the problem recurs, Shearer faces the prospect of being forced to hang up his boots at only 31.

This explains the search for another top-line striker, even though the Magpies are close to confirming the £6m capture of Coventry's Welsh international forward Craig Bellamy.

United boss Bobby Robson, who also has fresh concerns about the fitness of ankle-injury victim Carl Cort, has checked on a host of strikers, including Vitesse Arnhem's Victor Sikora and Anderlecht's Tomasz Radzinski.

But United have also enquired about Dutch international Kluivert, whose future at the Nou Camp is uncertain following the appointment of coach Carlos Rexach.

The Geordies made their interest known when they launched their move for Kluivert's Holland teammate Boudewijn Zenden.

However, United could face competition for Kluivert from Chelsea if Barca persuade the Stamford Bridge club to agree a swap deal involving fellow Dutchman Jimmy Floyd Hasselbaink.

Barca are understood to be keen to take former Atletico Madrid striker Hasselbaink back to Spain and are ready to use Kluivert as bait.

Ex-Leeds hot-shot Hasselbaink, who cost Chelsea £15m last summer and was the subject of an approach from Middlesbrough, rarely settles long at a club and Barca want him to spearhead their Champions' League challenge next season.

Meanwhile, Newcastle's move for Zenden looks to have hit a problem, with Serie A side Parma and Spaniards Deportivo La Coruna emerging as rivals for the 24-year-old winger.

Zenden's father Pierre, who also acts as his agent, admitted: "Some of the clubs showing an interest are in the Champions' League and that is obviously attractive.

"Nothing is decided, but it looks unlikely that Boudewijn will join Newcastle.''

But Newcastle expect to unveil Bellamy this week and Bolton left-back Robbie Elliott is set to rejoin United on a free transfer.