David Wilson was last seen outside Coral Island at around 3pm on Sunday, May 21.
The 40-year-old is said to have left hospital before receiving treatment and police are appealing for anyone who may have seen him to get in touch.
A spokesman for Blackpool Police said: "We are growing increasingly concerned about David. He left Blackpool Hospital prior to receiving treatment and it is urgent that we speak with him.
"If anyone has any sightings of David please contact Blackpool Police."
Anyone with information can contact police on 101 quoting log reference 879 of May 21.