Celtic pledged yesterday to keep Stilian Petrov as Fulham prepared to increase their £3.2 million offer for the Bulgaria captain, who is reported to be unhappy with the terms of his new contract offered by the club.

Peter Lawwell, the chief executive, who is handling Petrov’s negotiations, insisted that Petrov was “pivotal” to Celtic and declared that buying, rather than selling, was the principal task on Gordon Strachan’s agenda during the transfer window.

Petrov will not be heading to the Barclays Premiership, according to Lawwell, who spoke on Celtic’s website in the wake of the Tennent’s Scottish Cup holders’ humiliating 2-1 defeat away to Clyde on Sunday.

“I’ve read various reports saying that a number of our key players are heading out of the club, but I can reassure fans that there’s no truth in them,” Lawwell said.

“Contrary to some illinformed articles, players such as Petrov, [Neil] Lennon and [John] Hartson are absolutely pivotal to the team and are going nowhere.

“Stilian has 18 months remaining on his contract, John has at least 18 months and although Neil’s contract is up in the summer, we have had preliminary discussions with his agent on the way forward.

“Let’s not forget that, despite the obvious transition that the club is going through, we’re top of the league and are determined to do everything possible to regain the championship.

“Everyone’s hurting after a result like the one at the weekend, but it only makes the management and players even more determined to ensure that we deliver for our fans in the league campaign.

“Indeed, far from selling off our best players at such a crucial time, we’re already working hard to try and further strengthen the team during the January transfer window. We are keen to make further additions if we can get quality players in the right positions.”

The need to keep Petrov has been underlined by the failure to secure either De Jong or Steven Pienaar from Ajax. Strachan was keen on both midfield players, who are just 21, but Pienaar has moved to Borussia Dortmund and the German club have also spoken with De Jong about a possible deal. However, a Dutch newspaper, Algemeen Dagblad reports that Seville, of Spain, remains De Jong’s preferred destination.