The Netherlands international missed the end of Roma's season and the World Cup due to the anterior cruciate ligament injury, but made his first-team comeback in November.
After seven appearances in all competitions the 24-year-old endured another setback during Roma's 1-1 draw with Fiorentina on January 25.
Further surgery was required to rectify the problem, leading to reports that he may struggle to play regularly again, something he rejected on Tuesday.
"Contrary to reports in the media I am back in training and working hard on my comeback," he posted on his official Twitter account.
"Please don't believe people who have never seen me in their lives, but just follow the social pages of me and AS Roma where we will keep you updated on my progress.
"Just for the record, I'm right on schedule to be back when preseason starts."
