On your bike: Ronaldo gets over missing Juventus's Champions League opener by blowing kiss as he reveals new SKINHEAD look (VIDEO)

Five-time Ballon d'Or winner Cristiano Ronaldo has sung on an exercise bike, blown a kiss through a window and revealed his shortest ever haircut as he stays busy in quarantine following his positive coronavirus test.

The striker was forced to watch in isolation in Italy as Juventus won their Champions League opener 2-0 at Dynamo Kiev on Tuesday, when new loan signing Alvaro Morata deputized for the top scorer and netted twice in the second half to seal their victory in Ukraine.

Ronaldo held his hand to his chest, sang along to a ballad and shadowboxed while working out on an exercise bike indoors, blowing a kiss at girlfriend Georgina Rodriguez, who was filming his karaoke-and-fitness session from outside the window.

Instagram personality Rodriguez was captured shaving part of Ronaldo's hair in April, and her lover clearly enjoyed the experience enough to take a razor to his entire head of hair six months later.

Showing off his famously muscular physique in a pair of small pink shorts, Ronaldo posed on decking to demonstrate the shortest style he has ever adopted among the numerous hairstyles the Portugal captain has rocked over the years.

In a far cry from the ponytails and heavily-gelled looks he has previously worn, the 35-year-old has gone for an option favored by many during lockdown by having a neat all-over buzzcut.

Raising his thumbs and grinning for the camera, Ronaldo added: "Success in life is not measured by what you achieve, but by the obstacles you overcome."

After testing positive for Covid-19 just a day after sharing a snap with his Portugal teammates, Ronaldo was forced out of his nation's 3-0 Nations League victory at home to Sweden and has observed more than a week of his two-week quarantine.

He courted controversy when Italy's sports minister, Vincenzo Spadafora, appeared to accuse the country's most prominent Serie A star of ignoring quarantine rules by returning to Turin after his positive test.

Ronaldo insisted that he had observed the required guidelines and traveled back privately without making contact with anyone, and Rodriguez was the only visible figure in his latest social media post following his self-portrait while watching Portugal win in his absence.

Shortly after Ronaldo's post to his following of more than 241 million, Rodriguez shared her latest covershoot, for French celebrity magazine Paris Match, and told her 21.5 million followers that she "loved" the French capital.

The mother of Ronaldo's youngest son republished the shot of her partner on a bike in her stories, accompanying it with a heart and a pair of praying hands.

Fans joked that Ronaldo's new haircut was reminiscent of Brazil striker Ronaldo, who was also a hit in Serie A with Inter Milan and had a skinhead when he won the World Cup with his country in 2002.

Others complained that they would have to change his appearance on the recently-released new edition of computer game FIFA and compared his trim to Tottenham coach Jose Mourinho, his former boss at Real Madrid who shaved his head in a dramatic new look earlier this year.