There was a police presence in Lofthouse after a man was taken to hospital with serious head injuries.
People living nearby said that there had police cars outside a house in the area "constantly" since Monday evening.
They also said that forensic officers attended on Tuesday.
A West Yorkshire Police spokesman confirmed that on Monday, July 1, police were told about a man who was in hospital with serious head injuries.
The spokesperson said: "On Monday police in Leeds were informed about a man who was in hospital with serious head injuries.
"Officers have been carrying out enquiries to establish whether his injuries are the result of an assault or if there is another explanation.
"This has included examination of an address in Leeds Road, Lofthouse."