The 33-year-old Wales international had to be replaced at half-time by Aaron Mokoena, and boss Mark Hughes revealed the injury may require surgery.
Hughes said: "Robbie has tweaked his cartilage. He´ll have a scan and may need a small operation to tidy it up."
Copyright (c) PA Sport 2007, All Rights Reserved.
Do YOU want to write for GiveMeSport? Get started today by signing-up and submitting an article HERE: https://www.givemesport.com/writeforgms