Cristiano Ronaldo undergoes 'HBO' in bid to overcome knee injury - report

Real Madrid's Cristiano Ronaldo has visited a clinic while on holiday in Ibiza for hyperbaric oxygen therapy to speed recovery from his current knee injury, according to a report in Marca.

Ronaldo picked up the injury after a challenge from France's Dimitri Payet early on in the Euro 2016 final in Paris on July 10. The Portugal captain attempted to continue, but was soon stretchered off in obvious pain, although he returned to support his teammates from the touchline in extra time and then lift the trophy after Eder's late winner.

Neither the Portuguese FA nor Madrid have confirmed the extent of the injury but it has been reported as a ligament strain in his left knee, and that it will see him miss all of his club's preseason programme, including the UEFA Super Cup against Sevilla in Trondheim on Aug. 9.

Currently on holiday in Ibiza, where his luxury yacht was this week pictured close to that of Barcelona's Lionel Messi, Ronaldo has reportedly twice visited the Clinica Evidental -- a dental clinic which according to Marca also provides the hyperbaric oxygen therapy treatment as an additional service.

Marca's story on the visit says that inside the hermetically sealed hyperbaric chamber the player breathes pure oxygen at high pressure, which helps increase the oxygen level in the blood, and allows an injury to heal more quickly, but no real clinical evidence has yet proven it is actually useful.

"Thanks to hyperbaric medicine the regeneration of tissue and recovery from injury is stimulated, reducing in this way the risk of future injury and physical deterioration," an unnamed spokesperson for the clinic told Marca. "This speeds up the recovery time. Today this is one of the most effective complementary therapies in injury recovery."

Should Ronaldo miss Madrid's matches against Paris Saint-Germain, Chelsea and Bayern Munich during their U.S. tour, and also not play against Sevilla, he will have taken part in no pre-season games ahead of the kick of the new La Liga campaign.

Ronaldo has suffered from a series of knee problems in the past, with a tendonitis problem during the 2013-14 club campaign and 2014 World Cup putting his career at risk, although more recently that issue appeared to have eased.

The 31-year-old was hampered by a thigh problem before May's Champions League final, and appeared to be less than 100 percent fit during this summer's Euro 2016 finals in France. AS reported last month that he had asked Blancos president Florentino Perez to take his personal physio onto the club payroll, due to his difficult relationship with Madrid's current medics.