Eight machines were raided at JD Wetherspoon’s pub The Regal in the city centre after staff left without realising the perpetrator was still inside.
The criminal made his escape by smashing a window at 2:40am with a rucksack full of cash.
The large black bag would have been full of coins and notes, and Police are seeking anyone who witnessed him leaving the venue on 1 September.
Police have released CCTV images of a man they wish to speak to, who is believed to have been in the area at the time of the incident.
A spokesman for Wetherspoons said the pubco is relieved nobody was hurt in the incident while the operator will work with police to identify the perpetrators.
Anyone with information is asked to contact police on 101 or Crimestoppers, anonymously, on 0800 555 111 or via their website www.crimestoppers-uk.org.
At a separate incident in Preston, thieves were less successful after breaking into The Swan Inn on Church Terrace.
Leaving empty handed
Police have released CCTV images of two men they want to speak to following an attempted burglary.
On 7 September between 9.55-10.10am, two men slipped the lock and made a search before leaving empty handed in a silver or light blue car.
The men are both described as white. One man was wearing dark clothing and the other jeans, a jacket and a baseball cap.
PC Kristian Lowe of Preston Police said: “We are keen to trace the men and the vehicle in the CCTV images and I would urge anyone with information about the incident to get in touch with us as soon as possible.”
Anyone with information should contact police on 01772 209944 or 101 quoting log number 362 of September 7.