Cristiano Ronaldo is facing up to a month on the sidelines with an ankle sprain suffered on international duty.

The world's most expensive player returned to Real Madrid today for tests after limping out of Portugal's 3-0 World Cup qualifying victory over Hungary.

The club tonight confirmed that Ronaldo is facing several weeks out.

"After a clinical examination and an MRI scan, it is confirmed the player has suffered a recurrence of his injury to his right ankle, a medial collateral sprain with inflammation in the bone," the club said in a statement.

"The estimated (recovery) time is three to four weeks."