Superstar Cristiano Ronaldo is reportedly considering leaving Saudi Arabian side Al-Nassr in the summer, with a return to Europe or a move to the MLS.

The 40-year-old, who on a contract worth £488,000 per day, is the highest-paid footballer in history, began a strike earlier this week.

Ronaldo is claimed to be unhappy with the manner in which Saudi Arabia’s Public Investment Fund (PIF) is handling Al-Nassr’s finances, particularly in comparison to how they are treating rival clubs.

The PIF controls a 75 per cent stake in four Saudi Pro League clubs, Al-Ahli, Al-Ittihad, Al-Hilal and Ronaldo’s Al-Nassr, and has been the driving force behind the league’s ability to attract some of world football’s biggest names on lucrative contracts.

Al-Hilal completed the signing of Ronaldo’s former Real Madrid team-mate Karim Benzema on Monday, moving from fellow Saudi Arabian side Al-Ittihad.

Al-Hilal are currently one point clear of Ronaldo’s Al-Nassr in the Saudi Pro League, with the veteran Portuguese star said to believe his club have not been treated fairly in the transfer market.

Ronaldo reportedly claims Al-Nassr manager Jorge Jesus has not received adequate reinforcements compared to their rivals, despite Benzema’s move being funded by outside investors rather than the PIF.

Ronaldo launched an apparent strike on Monday, with the forward absent from Al-Nassr’s 1-0 win over Al Riyadh.

According to Portuguese newspaper Record, Ronaldo’s frustration has led to him considering leaving Al-Nassr in the summer.

The report claims Ronaldo has a £43million (€50m) release clause, with the veteran having 18 months to run on a two-year deal he signed last summer.

It remains to be seen whether any club would look to trigger the release clause, given Ronaldo is set to turn 41 on Thursday.