Patient is between 40 and 75 years of age with a clinical diagnosis of OA of the knee for more than 6 months prior to Visit 1 based on clinical and radiographic criteria, and being of American Rheumatism Association (ARA) functional Class I, II, or III. Patients should have an average pain level of between 4 and 8 on a Numeric Rating Scale (NRS) for at least 5 of 7 days before the randomisation, when answering the question: Please, rate the average pain in your index knee during the last 24 hours. Prior to the study, patients should have been using pharmacological treatments, such as Non-Steroidal Anti-Inflammatory Drug (NSAIDs), acetaminophen or weak opioids for their OA pain on a regular basis (defined as having used NSAIDs, acetaminophen or weak opioids at least 10 days out of 30 days during the last month prior to the screening visit).