Juventus manager Massimiliano Allegri remains optimistic of having Cristiano Ronaldo fit for the Champions League quarter-final against Ajax but will not rush the forward's return.

Ronaldo suffered a hamstring problem while away on international duty with Portugal.

Reports have suggested the 34-year-old aggravated the injury during his recovery with the Serie A club.

Before heading away with Portugal, Ronaldo helped the Bianconeri secure a place in the last eight of the Champions League with a stunning hat-trick to beat Atletico Madrid 3-0 in Turin and complete a remarkable turnaround.

Allegri confirmed Juve would not rush their star man back into action unless fully fit, with the runaway Serie A leaders set to play Cagliari away on Tuesday night.

"Cristiano Ronaldo is working to get back, we hope to have him ready for Ajax, but it will be difficult," Allegri told a press conference.

"The leg is much better. We still have nine days to go to the Amsterdam game and we have time to evaluate things. We must be careful in everything."

Full-back Leonardo Spinazzola is expected to be out for at least two weeks with a knee problem picked up during a substitute appearance in the 1-0 win over Empoli on Saturday.

"He won't need surgery. I believe everything will be fine and he will be available in 15 days," Allegri said.

Juventus hold a 15-point lead at the top of Serie A, while Tuesday's opponents Cagliari sit 12th, but Allegri is not taking the Sardinian side lightly.

"Tomorrow will be a difficult game, against a side that are strong at home," Allegri told a press conference reported by the club's website.

"Cagliari will look to make a good impression and it will be an interesting match.

"The team is in a good condition. In this period we will play every three days, therefore, it is fundamental to be able to rest.

"Juventus always has the great quality to bring the best out of players. This is fundamental for the growth of youngsters."

Cagliari manager Rolando Maran insists his side play every game to get a result as his side prepare to face the league leaders.

"This game has a special meaning," he told cagliaricalcio.com.

"The ranking is still to be improved, we must find continuity and we would like to give our fans another satisfaction.

"We must have the will to cultivate the dream within us. We play every game to get a result: this must be our mentality."

Maran believes the 3-0 win at Chievo on Friday took a weight off his side's shoulders but they will be without Lucas Castro and former Liverpool defender Ragnar Klavan for the Juventus game.