The Portuguese sat out the loss to Celta Vigo last week due to injury but is set to play in the final Liga game of the season
The Portuguese was injured during the recent draw with Real Valladolid and sat out last week's loss to Celta Vigo in a bid to rest ahead of the Champions League final.
However, he will be available when the Spanish giants host the Catalans as they look to finish the Liga season on a high.
"Cristiano Ronaldo will play because he is available and has no problems," Ancelotti told reporters.
"The team will be decided tomorrow. Only Pepe, Jese and Diego Lopez are not available. We'll give Sami Khedira some time because he needs it after a long period out.
"He did very well in Vigo for an hour and had no problems afterwards. He's an option for the Champions League final.
"[Asier] Illarramendi is the first choice for the final. He is used to playing there and was signed to play there. I haven't changed my mind.
"He has the quality to play every game, whether it's important or not."
Ancelotti is determined to deliver one last victory in the domestic season against Espanyol so they can approach the Champions League final in high spirits.
"We have a great atmosphere to help the team prepare for the final. We'll play with intensity because it is the last game in front of our fans. I think it will be a good atmosphere."