It could also be something as simple as tendonitis, that is inflammation of a tendon. If it isn't contraindicated I would try to take an anti-inflammatory if that doesn't help within 5-7 days you should call your doctor for follow-up. An actual tear of the muscle would be excruciatingly painful so you would definitely know if that was the case, but a strained muscle could be the cause. You can also try applying ice twenty minutes on twenty minutes off for the first 24-48 hours.
The reason of pain can be a tear muscle or pulled muscle. It can also be hamstring injury. Take muscular pain killers for three days and have complete rest. Also drink water with pint of table salt and juice of half lemon.