A thigh strain or quadriceps strain is a tear in one of the quadriceps muscles at the front of the thigh. It can range from a mild discomfort to a full blown tear of most of the muscle resulting in severe pain and inability to walk.
The breakage of the stitches starts within 2 weeks of the stitching but if you want the complete stitches to disappear then the process of hydrolysis or the enzymes in our body do that in a period of 60 days and therefore it approximately takes up to 2 months for the stitches to get dissolved.
When they take the stitches out, they might apply paper stitches to help keep the wound from opening while healing. At that time you should address the question with the doctor regarding his activities in the coming weeks. It should be sealed well enough within two weeks to resume normal activities.