Senior management has mentioned the size of the layoffs internally, but is by no means finalized and there is still a lot of negotiation to be done, the source added.
Airbus SE (AIR.PA) and Boeing Co's (BA.N) wide-body jets are powered by the company's engines and Rolls-Royce is paid by airlines based on how many hours their engines fly.
Earlier the Financial Times reported that Rolls-Royce was preparing to lay off as much as 8,000 of its 52,000-strong workforce.
According to the FT report, an announcement on the final figure is not expected before the end of May, when the firm will update employees. (On.ft.com/2VSaQfD) Rolls-Royce scrapped its targets and final dividend last month to shore up its finances to cope with the outbreak of the virus.
The company's chief executive Warren East said in April Rolls-Royce would be looking to cut cash expenditure by at least 10 per cent this year, including salary costs across its global workforce.
Discussions have just begun with unions over job cuts, the newspaper reported, citing sources.
It is still likely that the scale of job cuts will be larger than after 9/11 when the group cut 5,000 jobs and the vast majority of them are expected to hit the civil aerospace unit, the FT said.
While job losses are also expected in the operations of the unit in Singapore and Germany, the majority of the cuts are expected to be borne by the civil aerospace workforce in Britain, the report says.
Unite, the biggest trade union in Britain, did not comment in response to a Reuters query.