Barcelona must "find the formula" to give Lionel Messi a lucrative contract extension, according to the LaLiga champions' chief executive Oscar Grau.

Messi's current deal at Camp Nou expires in June 2018 and last month club president Josep Maria Bartomeu said the 29-year-old should be the best paid player in the world.

However, LaLiga regulations restrict the amount of each club's budget that can be spent on wages and, in light of the bumper deals handed to Luis Suarez and Neymar – both running until 2021 – Grau called for "a cool head and common sense" in negotiations he suggested could be influenced by a number of factors.

"We're working hard to renew Messi," he told reporters in Barcelona on Wednesday.

"We're keen to get it done and I am sure we will find the formula. By saying this I want to reassure supporters, because when you have the best it would be stupid to let him escape.

"It's a matter that has to be analysed with a cool head and common sense.

"Barca cannot spend more than 70 per cent of the budget on salaries, therefore we have make sure things balance. One option is to increase revenue, as we hope to with our strategic plan [to bring in €1billion annually by 2021].

"We want to have the best, but we must always prioritise. The objective is for the best player in the world to stay at Barcelona and it's the same with everyone, although especially with those that were formed in La Masia, who I think should retire here."

Barcelona have been linked with a move for experienced Shakhtar Donetsk right-back Darijo Srna during the January transfer window, while midfielder Ivan Rakitic was linked with a switch to Manchester City over the weekend having fallen out of Luis Enrique's first XI.

In line with the budgetary balancing act he outlined, Grau added there would be no incomings without outgoings at Camp Nou before the mid-season window closes.

"It's a matter we want to work on with discretion, while keeping our budget in mind," he said.

"If there are no outgoings, though, there will be no incomings. If an opportunity comes up, we will look into it."