Barcelona’s hopes of offering Lionel Messi an improved contract face a stumbling block because of the expenditure caps imposed by La Liga, according to the club’s chief executive, Òscar Grau.

Whereas Luis Suárez and Neymar have each signed new deals until 2021, the Argentinian’s contract expires on 30 June 2018, giving Barcelona 18 months until he would be able leave the club for free.

Messi earns a reported €22m (£19m) a year after tax from Barça, whereas Neymar’s and Suárez’s salaries are believed to be about €25m after their latest contract renewals. Grau said any new deal for Barcelona’s all-time top scorer would put considerable pressure on the club’s finances.

“Barcelona has to analyse this situation with a cold head and common sense,” Grau said on Wednesday. “Barça can’t exceed 70% of its budget on wages and therefore we have to make the numbers add up.”

La Liga agrees budgetary limits with each club at the start of every season and its regulations ensure its clubs only spend a certain proportion of their budget on wages.

Barça’s budget for this season is €695m. They pay the highest wages in Spain and the second-highest in world football behind Manchester United, according to the latest publication of the Global Sports Salary Survey, which reported that Barcelona players earned an average annual wage of $7,456,800 (£6.1m).

Grau hinted that Barcelona may need to raise funds by selling players, as well as strengthening the club’s commercial income. Their latest sponsorship deal with the Japanese retailer Rakuten, the biggest such deal in the sport, will earn the club €55m a year.

“One option is to increase our revenues, as our economic strategy forecasts,” Grau said. “We want to have the best players around, but perhaps we have to prioritise.

“The club wants the best player in the world to stay at Barça. I would like to ease the concerns of club members and supporters but we have to use common sense.”