Dog emergency surgery

Our dog named batman had an incident fighting with a cat from street. The cat attacked our dog at his left front leg and probably her claws was injected with something dirty, we didnt give much attention to this cause the wound was small. Our dog after 3 days couldnt walk well and didnt had appetite, we took him to a doctor and he told us that we must do a surgery in the last 30 days, we lack of money we are a familly of 4 including my mother and we are orphans from father side so we cant gather this ammount.

Please help us.