In fairness he did have an operation on it, so I suspect it was real.
I don't mind him moving on after 2 years if that was the agreement he had with the club (which it appears to be). But that was with the tacit understanding that he'd give 2 good years of service to Saints. But he didn't. He missed a large chunk due to the injury, while receiving wages and treatment by the club. So I don't think it's unreasonable to repay that and give one more (hopefully injury-fee) year for us before moving on (at presumably a much higher price if he performs well next season).