Police are appealing for witnesses to the armed robbery at the Spar convenience store on Worsley Mesnes Drive, Worsley Mesnes, shortly before 7am on Thursday January 20.
They established that at least two men entered the shop and threatened a staff member to open the shop till.
He refused and it was at this point that he was assaulted with the liquid.
The offenders then made off with a large quantity of cigarettes down an alleyway to the side of St James CE School towards Cornwallis Road.
The victim's injuries are not believed to be life-threatening.
He did not require hospitalisation and was treated at the scene for an injury to his eye.
A crew from Wigan fire station was on standby in case the substance proved to be particularly noxious but it was stood down when it was realised that there was not a greater threat to public health.
Inquiries are ongoing and no arrests have been made.
Anyone with information is asked to report it online by using the LiveChat service at www.gmp.police.uk quoting log number 478 of 20/01/22.
Alternatively, contact Crimestoppers anonymously on 0800 555111.
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