Strootman has only played six league games since returning to action in November after suffering ligament damage which sidelined him for eight months and forced him to miss the World Cup.
"The scar tissue from my previous operation has been removed successfully today," Strootman said on Twitter on Friday.
"Unfortunately some cartilaginous damage... was found too. This means I have to take a longer rest period than anticipated earlier.
"I am extremely disappointed that it will take much longer before I can be back on the pitch again."
Strootman underwent arthroscopic surgery in Amsterdam on Friday after suffering a knock on the knee during the 1-1 draw against Fiorentina at the weekend.
He previously said it was just a case of removing some scar tissue.
"The surgery allowed to prove and confirm the stability of the new ligament as well as to remove exceeding fibrotic tissue present in his knee," said Roma in a statement.
"Also, the surgery showed a cartilaginous lesion which required surgical treatment. The player has already left the hospital and will follow a convalescence period at home.
"He will start the rehabilitation process after further clinical checks."
(Writing by Brian Homewood in Berne, editing by Pritha Sarkar)
Share
