Real Madrid forward Cristiano Ronaldo is to undergo stem cell therapy in a bid to speed up his recovery from a hamstring problem. The 31-year-old striker suffered an injury during Real's league win over Villarreal on 20 April and has missed the club's last two matches, including the Champions League semi-final first leg against Manchester City.

Spanish daily AS reported that the Portuguese striker will definitely miss the weekend trip to Real Sociedad and is doubtful for the second leg against City on 4 May. The paper claimed Ronaldo had grown "tired" of Real's medical department and had visited a private clinic in Madrid on 27 April to have scans.

He will reportedly be treated with stem cells to regenerate damaged tissue in his thigh, with his recovery monitored by the club's medical staff. Real have kept quiet on Ronaldo's condition since Zinedine Zidane said the Portuguese "felt something" before the City match.

The Champions League semi-final tie between the two teams is evenly-poised after a goalless draw in the first leg at the Etihad.

Real talisman

Ronaldo is the top scorer in the Champions League this season and his absence in next week's deciding leg would provide a massive lift to Manuel Pellegrini's side, who are bidding to reach their first ever Champions League final. The 31-year-old claimed that he would have played the first leg if it had been a final.

Karim Benzema wins the ball
Karim Benzema (left) is a doubt for Real Madrid\'s La Liga encounter with Real Sociedad Getty Images

"It's sensible; I'm going to wait for the next game. If it were a final, I'd play," he was quoted as saying by Marca on 26 April. His mother, Dolores Aveiro, told the paper: "Right now he is 80%, but I hope that by next week he will be 100%."

Meanwhile, Karim Benzema is also racing to be fit for the second leg after he sustained a hip problem at the Etihad. AS said the Frenchman would sit out the Sociedad match due to the injury.