My pet rat seems to be injured! Please help me!?

My pet rat Sebastian was playing with his brother when I was cleaning out their cage. I opened the travel cage I keep them in when I clean the cage, and it seems he was injured somehow. He generally never squeaks and now he does every time I touch him or as he wanders around. He seems to be really hurt somehow, as this has now continued for around 5-10 minutes, it is not normal and he sounds really distressed. He can walk alright and doesn't seem to be avoiding the use of any limbs, however his tail is slightly lifted. PLease help if you have any ideas or if this has happened to you! Thank you!