Cristiano Ronaldo's return to fitness could be vital to Juventus's bid to end their Champions League drought going back 23 years as they head to Ajax on Wednesday with uncertainty over whether their superstar will play or not.

Ronaldo hasn't played for the Serie A leaders -- who are just one point away from sealing an eighth Italian league title -- since scoring the sensational hat-trick that saw Juve come back from a 2-0 first-leg deficit to knock out Atletico Madrid last month.

He was rested in the subsequent 2-0 league defeat at Genoa and then picked up a thigh injury on international duty with Portugal two weeks ago.

But coach Massimiliano Allegri remains confident the 34-year-old will be ready for Wednesday's game in Amsterdam.

"He (Ronaldo) always feels ready. We are confident of having him at Ajax on Wednesday," said Allegri after Saturday's 2-1 league win over AC Milan.

The five-time Ballon d'Or winner joined his teammates for training on Monday and is expected to travel with the team to the Netherlands.

Portuguese teammate Joao Cancelo, himself recovering from a calf strain, believes that Ronaldo will be present.

"Cristiano's training, he's a serious professional. He has committed himself to do everything possible to be there and help the team," right-back Cancelo told Sky Sport Italia.

"I really think he'll be called up, after that we'll see if he plays from the first minute or if he will come on later. The coach will decide."

Ronaldo himself has given no updates on his injury, apart from a short video posted on his social media accounts, looking relaxed as he drove his car and singing along with his partner Georgina Rodriguez and son.

PSYCHOLOGICAL BOOST

Ronaldo's presence would be a physiological boost for Juventus who signed the Champions League goal king for 100 million euros ($117 million) last summer and agreed to pay him a 31 million-euro annual salary to end their search for the title they last won in 1996.

Ronaldo is the only player to have won the title five times and is the record goalscorer in the competition with 124, including 15 last season.

The Italian champions were beaten finalists in 2015 and 2017, with Ronaldo on target for Real Madrid in the latter.

This campaign, Ronaldo was sent off in the opening group game against Valencia, with only one goal against Manchester United before his spectacular hat-trick against Atletico.

But he brings further energy and enthusiasm to the team.

Allegri predicted after last month's two-goal defeat in Madrid that Ronaldo would pull them through in Turin, and he duly delivered.

"In matches of this kind he gets really excited and enthusiastic, having him gives us a great advantage," Allegri said.

The Portuguese ace's on-pitch performance had been unaffected by off-pitch concerns including an investigation of rape allegations against him in the United States dating back to 2009 which he vehemently denies.

"This is why Juventus bought me, to help them in games like this," said Ronaldo.

In the case of Ronaldo's absence Allegri would most likely line up with Mario Mandzukic, Federico Bernardeschi and Paulo Dybala.

Teenager Moise Kean also offers Allegri a goal-scoring option as he has burst into the limelight in Ronaldo's absence with five goals in as many league games.

Winger Douglas Costa also looks close to a return from a recurring muscle injury.

But Germany's Emre Can, suffering from an ankle sprain, will miss the trip as Juventus and Ajax play for the first time in 16 years.