Ronaldo - who has been nursing a thigh strain - has not played for Juve since he scored a hat-trick against Atletico Madrid in the last round on 12 March.

Giorgio Chiellini misses out with a calf strain, while Emre Can also stays behind with an ankle issue.

Ajax have no fresh injury concerns before the first leg in Amsterdam.

Can Ronaldo help bridge the gap in Europe?

Juventus are just one point away from winning an eighth successive Serie A title, but they have failed to win the Champions League since 1996.

Ronaldo, 34, has been sidelined since he was injured playing for Portugal in a Euro 2020 qualifier against Serbia on 25 March.

The Portuguese forward was bought last July to help Juventus attempt to become champions of Europe, the Italian club having reached two of the past four finals.

Allegri says Ronaldo will start at the Johan Cruyff Arena "as long as nothing happens tonight or tomorrow morning".

"Cristiano has trained with the team and is available," said the Juve boss.

Despite his absence, Juventus can win Serie A with six games to spare if they secure a draw at SPAL in their next league match.

"Cristiano looks the same as ever. He's in good shape, a very important player for us, as everyone knows, and we are happy he'll be with us tomorrow," said defender Daniele Rugani, who is set to start in the absence of the veteran Chiellini.

Ajax are the surprise - Ten Hag

Manager Erik ten Hag says his side are happy to be the "surprise" package in this season's Champions League quarter-final.

The Dutch side, who beat defending champions Real Madrid in the last round, have not reached the last eight since 2003.

"For a country like the Netherlands, it's really difficult to get to this stage," said Ten Hag.

"Financially, the circumstances have really changed in recent years."

Ajax have not only transformed their fortunes in Europe, but they also ended a 1,060 day wait to return to the top of the Eredivisie table with a thumping 5-2 victory over FC Emmen on 3 April.

"A couple of months ago, we found our form and returned to being a strong team," said Ten Hag.

"It will be another big obstacle to overcome after Real, but we will play as usual and we will have to be good at reading the game."

The sides will meet again in the return leg in Turin on 16 April, with the winners playing against Manchester City or Tottenham Hotspur in the semi-final.

Match facts

Head-to-head

• Ajax and Juventus will be facing for the ninth time in the European Cup/Champions League and for the first time since November 2004. The Dutch side have not beaten the Italians in the competition since winning the 1973 European Cup final in Belgrade (1-0).
• Juventus are unbeaten in each of their past nine European matches against Ajax (W5 D4), including a draw in the 1996 Champions League final before going on to lift the trophy thanks to a penalty shootout victory.
• Ajax will host Juventus in a Champions League encounter for the first time since September 2004 in the group stages, when they fell to a 0-1 defeat thanks to a Pavel Nedved strike for the Italians.

Ajax

• Ajax knocked out defending champions Real Madrid in the last round; indeed, the last side to knockout the current holders of the Champions League was Atletico Madrid (v Barcelona) during the quarter finals in 2015-16, going on to lose in the final against Real Madrid.
• They are the first Dutch side to reach the quarter-finals of the Champions League since PSV in 2006-07. Indeed, Ajax find themselves at this stage for the first time since 2002-03, when they were eliminated by AC Milan.
• Ajax have had a younger starting XI on average (24 years 202 days) in the Champions League this season than any other side left in the competition.

Juventus

• Juventus have reached the quarter-finals of the Champions League for the third successive campaign, their best such run in the competition since doing so in four successive seasons between 1996 and 1999.
• Only Lionel Messi (11) has had a direct hand in more goals in this season's Champions League than Ajax's Dusan Tadic (nine - six goals, three assists).
• Juventus striker Cristiano Ronaldo has scored seven goals in his past four Champions League matches against Ajax, including a hat-trick for Real Madrid on his last visit in October 2012.
• Only against Bayern Munich (nine) and his current side Juventus (10) has Cristiano Ronaldo scored more Champions League goals than he has against Ajax (seven).