The Portuguese international has 12 months remaining on his current contract with Juventus but has been heavily linked with a move away from Italy.
Allegri has returned to Juventus after the sack of Andrea Pirlo and wants to do well in his second coming.
And with Ronaldo's future being in the dark, Allegri has insisted the five-time Ballon d'Or has ensured him of staying at Juventus.
"Let's clarify this issue, Ronaldo told me that he's staying," Allegri said in response to numerous questions on Ronaldo's form and mindset ahead of Sunday's Serie A opener at Udinese.
"He has always trained well and has always been available. I've read rumours in the papers, but he's never wanted to leave Juventus."
Ronaldo, since arriving at Juventus on a four-year deal for a reported €112 million transfer fee in 2018, has been unable to lead the Italian team to a Champions League title, a competition he won four times with Real Madrid.
The former Manchester United forward won the Serie A title in his first two seasons with the Old Lady, but missed out on the title to Inter Milan as Juventus finished 4th in the league.
Ronaldo in May, became the fastest player to score 100 goals for the Italian side in 131 games.
He finished last season with 29 goals as the league's topscorer with three assists.
Despite missing Juventus' final friendly game against the club's youngsters on Thursday, Ronaldo will be in action for the season opener when they travel to Udinese on Sunday.
