post radical prostate surgery

My husband had radical surgery for prostate cancer bout five weeks ago. He recovered well and returned to work last week. While at work, a colleague asked his help in lifting something. He didnt think, and went ahead and gave him the help. Now he has pain in the area of his incision. It hurts only when walking, not while sitting. His incontinence is still decreasing daily, so that is not a concern. Just this pain. What kind of injury might he have done to himself?

We appreciate any advice, as this is very worrisome!
Thank you,
Azile