Hello. Last Night My Two Year Old Seemed To Be

Hello. Last night my two year old seemed to be limping and was not putting pressure on her right leg. When she walked, she kept her right leg bent & used her tipy toes on right foot only. Today is the same thing. She is not crying & has no fever. She cannot straighten out her right leg. When I try to have her extend it, she cries. But when it is bent or bent towards her chest, she's fine. What could be wrong?