Ronaldo, Real's all-time top scorer with 371 goals in 360 games, will sign the new deal on Monday at the Santiago Bernabeu Stadium before giving a news conference.
Ronaldo is reported to be in line for an increase on his current salary, estimated to be 21 million euros ($23 million), making him the highest-paid player at Real Madrid.
The Portuguese has collected one La Liga title, two King's Cups and two Champions League titles since joining Real from Manchester United in 2008 for a then world record 96 million euros but has had an inconsistent start to the current campaign.
The forward failed to hit the target in a near anonymous display in Real's 3-0 win over Leganes on Sunday to mark five games without scoring at the Bernabeu, his longest run without a goal in front of Real's fans since he joined the club.
Ronaldo's last goal at the Bernabeu came against Sporting Lisbon in the Champions League on Sept. 14. His only goal there in the league was against Osasuna on Sept. 10.
Ronaldo has scored seven goals in the league and Champions League this term and made amends for his worst start to a season since joining Real by hitting a hat-trick in last week's 4-2 win away to Alaves.
The 31-year-old missed a series of chances against Legia Warsaw on Wednesday, however, and was seen venting his fury at Bale for not passing to him in the second half against Leganes.
"Nothing is up with Cristiano, we always want him to score and at Alaves he scored three and that's that," said Zidane.
"He always wants to score but it doesn't matter if he doesn't once in a while. I think he's playing well, working hard for the team. He obviously always wants to score but I think he's relaxed about it."
Despite the player's current inconsistency, Zidane expressed his delight at Ronaldo extending his stay at the club.
"I'm happy because he's the type of player who deserves to finish his career at Real Madrid," said Zidane, who saw out his playing days at the Bernabeu and was infamously sent off for France in the 2006 World Cup final in his last ever game.
"He's unique. His dream is to retire here, wearing this great white shirt, just like I did."
(Reporting by Richard Martin in Barcelona; Editing by Toby Davis and Clare Fallon)
