But the Teessiders insist they have not had any approach, and have warned Pompey that if they make a move, it will be summarily rejected with new manager Gareth Southgate having big plans for the former Maccabi Haifa hitman.

Chief executive Keith Lamb said: “Any reports linking Yakubu with Portsmouth have been put into the public domain by mischievous and disreputable agents who are seeking to manufacture a move for their own selfish ends.

“I can confirm that there has been no contact from Portsmouth, nor do we want any. Having spoken to the manager, I know Yakubu figures prominently in our future. Gareth plans to speak to Yakubu to reassure him – if reassurance is necessary – just how important he is to our future.

“We repeat that he is not for sale, nor is any of our other young stars. As we have said before, we’re building a team, not dismantling one. The arrival of Robert Huth, a 21-year-old international defender, is evidence of that.”

Yakubu came within a whisker of being the first Boro striker to break through the 20-goal barrier since Fabrizio Ravanelli in 1996-97 last season, although a barren spell at the end of the campaign saw Jimmy Floyd Hasselbaink and Mark Viduka renew their partnership.

Southgate, currently working for ITV at the World Cup in Germany, told the club’s official website, www.mfc.co.uk: “Yak is not for sale.

“He is a massive part of our plans, not just for next year, but beyond. I rate Yak very highly. He scored 19 goals last season and has been one of the leading Premier League scorers for the last few years.

“What’s more, we believe he can get even better.”