PORTSMOUTH last night tabled a £12m bid for Middlesbrough striker Ayegbeni Yakubu - just hours after the Teessiders completed the capture of Turkey international Tuncay Sanli.

Despite having had a £10m bid for Yakubu's services turned down last summer, the south-coast club have made renewed contact with Middlesbrough officials in an attempt to capture Harry Redknapp's leading transfer target.

And with Pompey set to test Boro's resolve to the full, sources close to Redknapp have claimed that long-term Middlesbrough target Gary O'Neil has also been offered as a possible makeweight in any deal.

Boro officials are expected to resist Portsmouth's latest offer, just as they turned down the same club's eight-figure approach at the turn of the year.

But with Yakubu understood to be keen on a return to his former employers, and with manager Gareth Southgate having admitted that "every player has their price" earlier this summer, it remains to be seen whether the Teessiders can continue to rebuff Portsmouth's persistent interest.

Despite the impending arrival of both Tuncay and Jeremie Aliadiere, the loss of Yakubu would represent a crippling blow ahead of the start of next season.

He has scored 35 goals in 86 starts since making a £7.5m move to Middlesbrough in July 2005 and, while he did not find the net as he went off the boil in the final three months of last season, the recent departure of Mark Viduka has made the retention of his services all the more imperative.

Unfortunately, it is not as simple as that, with Yakubu's growing unease on Teesside accompanying a financial situation that could make his sale this summer all the more appealing.

Boro are due to pay the final instalment of the 24-year-old's transfer fee to Portsmouth this August - a sum that is believed to be worth around £2.5m - and it is understood that this fee would effectively be written off if the striker was to return to Fratton Park in the intervening period.

Therefore, an offer of £12m is effectively a £14.5m bid with the transfer balance taken into account.

The arrival of O'Neil would help to soften the blow, but that is equally complicated situation with Boro understood to value the midfielder at around £4m.

Portsmouth claim to have already turned down a £6m offer for the 24-year-old this summer, but it is extremely unlikely that Middlesbrough would value him as highly.

Last night's developments came as the Teessiders were congratulating themselves on their successful pursuit of Tuncay.

The 25-year-old Turkey international will travel to Teesside for a medical next week after agreeing personal terms with Boro chief executive Keith Lamb on Tuesday evening.

Tuncay, who became the first Turkish player to score a Champions League hat-trick when he scored all three goals in a 3-0 thrashing of Manchester United in 2004, will make a free transfer from Fenerbahce.

With Aliadiere also expected to undergo a medical at Rockliffe Park within the next seven days, Boro's new-look forward line was beginning to take shape before Yakubu's future was called into question once again.

As well as restructuring his forward line, Southgate is also attempting to strengthen a defence that has lost Abel Xavier and Stuart Parnaby this summer.

Long-term targets Jose Bosingwa and Philipp Degen remain on his radar but, with both players proving difficult to prise from their current employers, AZ Alkmaar full-back Gretar Steinsson has emerged as a leading alternative to fill the vacant right-back berth.

The 25-year-old Iceland international, who was part of the Alkmaar team that knocked Newcastle out of last season's UEFA Cup, is keen to move to the Premiership, and Boro are one of a number of clubs to have inquired about his availability.

Steinsson has established himself as a leading member of Louis van Gaal's team since moving from Young Boys in 2005, but his employers have hinted he may be allowed to move for around £3m.

"Gretar is really happy in Alkmaar, said his agent, Jerry de Koning. But it is his ultimate dream to play in England. The English style of football is perfectly suited to him."

Meanwhile, Boro chairman Steve Gibson has confirmed that he will ask the Premier League for further dispensation to allow Southgate to continue as manager next season.