The Brazilian playmaker is tipped to get a start at the Bernabeu with the Champions League last 16 second leg at United on Tuesday taking priority for a Real side 16 points adrift La Liga leaders Barca.
"The coach hasn't said who will play yet. He will decide tomorrow. If I play, it could be a good opportunity for me," Kaka told a news conference on Friday.
"It could be a chance to show that in important games, like a 'Clasico', I can still make an important contribution to the team."
A string of injuries hampered him when he first arrived in Spain and since then the 29-year-old has dropped down the pecking order behind the likes of Germany midfielder Mesut Ozil and Croatia's Luka Modric.
"It hasn't been easy," he said. "I have been a professional for 11 years, seven or eight of those as a regular starter at club level and in the national team.
"To pass from being a protagonist to being, in inverted commas, a normal player, is tough, but it has helped me to mature on a personal and professional level."
Real crushed holders Barca 3-1 at the Nou Camp on Tuesday to set up a King's Cup final with Atletico Madrid, and Kaka said the manner of their victory had been a morale-boost to the team.
"Tuesday gave us a lot of confidence," he added. "Now we need to look to reduce the advantage Barca have on us from 16 to 13 points. We aren't motivated to try and push them into a crisis, only of winning each game.
"The team has proved they can get results wherever it may be, at the Nou Camp or Old Trafford. Let's see if tomorrow we can get a bit more confidence."
"I have two years left on my contract," he said. "I am happy to continue at Real, but I don't want to be a problem for the club. If I have to go, I will go.
"I don't know if I will get back into the national team, but I have to be prepared. I would love to return. There is still time."
