The incident resulted in a penalty for Real in the Champions League match two weeks ago, Diawara was sent off and Ronaldo suffered a sprained ankle.
"I am sad and it's something that has been torturing me as it was never my intention to hurt him," Diawara told Spain's As newspaper on Tuesday.
"The tackle at the Bernabeu was not necessarily a penalty. I took the ball first and the footage shows that," he added.
Ronaldo recovered to start Portugal's World Cup qualifier against Hungary on Saturday but aggravated the injury and limped off. Real said he would be ruled out for up to four weeks.
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