The late offer has already shifted a council planning consultant's view on Senescura Ltd's application for up to 182 units of care accommodation and a 75-bed nursing home and dementia unit at the Hencote estate off Ellesmere Road.
A Government planning inspector's decision on the matter is set to be crucial as experts line up to make their arguments.
A spokesman for Shropshire Council said: "The appellant has offered a £1.3m affordable housing contribution at a very late stage in the process.
"The Local Planning Authority’s position was that it was too late and that the inquiry should proceed without the contribution.
"The Inspector has decided to continue with the inquiry but also consider the contribution."
In communications with the planning inspectorate, Shropshire Council's own planning witness Kelvin Hall has said the contribution to affordable housing means the "adverse impacts no longer significantly and demonstrably outweigh the benefits of the development."
Government inspector Louise Nurser's decision on the matter will be crucial. If she decides that the offer is good then the council looks set to offer no evidence on planning matters.
The council has told the inspector that its primary position is that the inspector should not consider the affordable housing contribution.
But if she does then the council's "evidence to the inquiry will be that there are no reasons to withhold permission subject to the inclusion of the affordable housing contribution."
The council has been promoting the inquiry for some time and inviting objectors to have their day.
Objector and Winney Hill campaigner Ben Jephcott thinks it "would be an outrage".
He has asked Shrewsbury Town Council at its meeting tonight to "make sure the case against is at least heard".
He continued: "How can the inquiry go ahead in any realistic way if Shropshire Council offers no evidence?"
As well as impacts on Winney Hill, and traffic on Ellesmere Road, one of the biggest fears of objectors to this plan is the knock on effect it will have on our NHS and social care in Shrewsbury and Shropshire.
"As reported in the Shrewsbury Chronicle, 20 per cent of care beds in Shropshire are empty because of staff shortages.
"The Hencote nursing home and extra care units would increase demand for nursing staff considerably. It is a high end development aimed at attracting very elderly but affluent residents needing care from all over the country, it will not meet local needs."
The planning inquiry's first day on Tuesday is set to be broadcast from 10am on YouTube here: youtube.com/watch?v=UKcHNlBbQ4Q