Police are investigating an aggravated burglary in the early hours of Thursday (March 21) at a property in Gresham Walk, Crawley.
Around 12.45am a man came into the property and attacked a 19-year-old man with a bat. He was treated at hospital for head and arm injuries.
The suspect, who fled the scene, is described as white with blonde hair and in his 20s.
Detective Inspector Colin Garman said: "The victim has some serious, but not life threatening, injuries and remains in hospital. We are appealing to anyone who saw someone enter the property or was seen running away to contact us."