The 34-year-old Juve attacker hobbled off 30 minutes into Monday's stalemate after pulling up chasing a ball on the left wing, and Turin-based daily Tuttosport launched a "Ronaldo Alarm" on Tuesday, while Gazzetta Dello Sport headlined with "CR7 Worry".

Ronaldo underwent tests in Portugal on Tuesday with Juventus moving to allay fears afterwards by issuing a statement to say the injury was a "minor" one.

"Cristiano Ronaldo underwent examinations in Portugal that showed an apparent minor injury to his right thigh flexors," the Serie A giants said in a statement.

"His condition will be monitored and will be subjected to new investigations to define the resumption of competitive activity."

Juventus travel to Amsterdam for the first leg of their quarter-final clash with the Dutch side on April 10 with the return leg on April 16, and the absence of Ronaldo would be a huge blow for the Turin giants after he dragged them past Atletico Madrid in the last 16 with a return-leg hat-trick earlier this month.

Recovery time for a thigh injury varies from up to 10 days for a slight problem to three months, but Ronaldo quickly moved to reassure everyone that he would soon shake off the knock.

"I'm not worried. I know my body. I believe that in no more than two weeks I'll be fine," Ronaldo told reporters.

"We have to wait 24 to 48 hours".

The Portuguese star is set to undergo further tests in Juve's medical centre in Turin.

- Resilient Ronaldo - 

Ronaldo was rested two weeks ago when the Italian champions suffered their first league defeat this season, 2-0 against Genoa in their last game before the international break.

But Juventus have a comfortable 15 point-lead on the top of the Serie A table and are on course for an eighth consecutive Scudetto.

Juventus signed the five-time Champions League winner last summer for 100 million euros ($117 million) to end their search for the title they last won in 1996.

His hat-trick against Atletico sealed a place in the quarter-finals with a 3-2 aggregate win after being two goals down after the first leg.

The five-time Ballon d'Or winner has rarely been injured during his long career.

He suffered two injuries to his left ankle in 2008-2009 and 2009-2010, with his last serious injury a cruciate ligament sprain in his left knee during the Euro 2016 final, won by Portugal against hosts France.

The Genoa defeat was the only time Juve coach Massimiliano Allegri has rested Ronaldo this season but he has other attacking options available, including Argentine Paulo Dybala, who has been overshadowed by Ronaldo this season, and rising start Moise Kean, 19, fresh from scoring his first international goal with Italy against Finland.