The victim, a woman in her 20s, reported a man had subjected her to a serious sexual assault at an address in the city.
Following CCTV enquiries, police would like to speak to the man pictured.
He is described as of south Asian heritage, mid to late 20s and of slim build.
Det Sgt Hana Alayli-Moore of Lancaster CID said: “This a very serious offence and I believe someone will recognise this man.
“The victim is being given continued support by officers and we want to trace the man pictured as soon as possible.
“We believe he may work or may have worked in the Lancaster area.
“If you have any information please call us immediately.”
Anyone with information can call police on 101 or email [email protected] quoting log 1488 of November 22.
The attack happened on November 22 2021 but police have only now issued the appeal.