The 32-year-old guard was stabbed while making a cash delivery to the Tesco store in Northgate, Cleckheaton, West Yorkshire, on 12 November.
Detectives said he was "ferociously attacked" with the knife even after the two robbers had got hold of the cash.
They hope to get fresh information after firm G4S put up the reward.
"These are clearly dangerous people who are prepared to use extreme violence unnecessarily and they need to be caught"
The security guard was seriously injured and spent weeks in hospital before continuing his recovery at home.
A 28-year-old man who was arrested over the robbery last year answered bail last week and has been released without charge.
Det Insp Lisa Atkinson, who is leading the investigation, said: "A totally unwarranted level of violence was used by these men and it is important that we trace them as soon as possible.
"The fact that the guard was stabbed when the offenders had already got the money is particularly disturbing.
"We have had some very positive lines of enquiry and received some good information. However, we need further assistance from the public to bring these people to justice.
"These are clearly dangerous people who are prepared to use extreme violence unnecessarily and they need to be caught."
The two robbers left the supermarket in a stolen black Seat Leon, driven by a third man.
The car was found abandoned later on Birkett Street and the robbers are thought to have escaped in a silver Audi estate.
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