The Argentina international has just returned from two months on the sidelines with a hamstring problem picked up against Borussia Dortmund in the Champions League two months ago.
He played his first minutes since then as a substitute in Wednesday's King's Cup win over Celta Vigo, when Ronaldo inspired the side to a 4-0 victory and a place in the quarter-finals against Valencia.
"I am feeling good. They have been two hard months. I am available and able to play the full 90 minutes," Higuain told a news conference on Friday.
Higuain is still Madrid's second highest scorer in La Liga with seven goals despite his time on the sidelines, with his strike-partner Karim Benzema struggling in front of goal on five so far.
Ronaldo, who was runner up Lionel Messi in the World Player of the Year awards on Monday, has carried the team to victory with two inspirational performances in the last week and has scored five goals in their two games since the mid-season break.
"I don't know if he is in his best run of form," Higuain said of Ronaldo.
"He's been scoring more than 40 goals a season since he arrived here and we are pleased he has been doing well.
"We have been going through a tricky patch and his goals have helped us to win the games. When it comes together for him, it's good for all of us."
Real head to Pamplona without Ronaldo, and their first-choice centre-backs Pepe, who is injured, and Sergio Ramos, who was hit with a five-match ban on Thursday after being sent off and insulting the referee in the Cup against Celta.
With reserve keeper Antonio Adan suspended, Iker Casillas will be back in the starting line-up, while full-backs Fabio Coentrao and Marcelo returned to the squad after injury.
"Every player is important and we can't dwell on those who are missing," the 25-year-old said.
"We have to replace them, and we have players who can do that very well."
Real have slipped 16 points behind unbeaten leaders Barcelona, and are five behind second-placed Atletico Madrid, ahead of a traditionally tricky fixture for the bigger clubs.
Osasuna's compact Reyno de Navarra stadium, with their vociferous fans right up alongside the pitch, has been an uncomfortable venue for both Real and Barca in recent seasons.
Real have one win, a draw and two defeats from their last four trips there.
"It has always been difficult to play there, apart from last season when we won comfortably," Higuain said. "It's a tough stadium and they are in need of the points."
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