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.
"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."
"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."
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.
"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."
