The phrase "a significant downgrading" is correct and usable in written English.
It can be used when discussing a notable reduction in quality, status, or value of something.
Example: "The recent changes in management have led to a significant downgrading of the company's reputation."
Alternatives: "a major decline" or "a considerable reduction".
This final acknowledgement follows weeks of growing pessimism and represents a significant downgrading of the summit's original goal.
His presidency has introduced a distinctly negative tone toward Russia, amplified by a contentious espionage dispute and policy debates that seem headed toward a significant downgrading of relations.
In a significant downgrading of expectations, the European Commission said gross domestic product would shrink by 0.3 percent for the 27 members of the Union as a whole and by 0.4 percent for the 17 countries in the euro area.
The government's review of the future of the Trident submarine nuclear missile system is likely to suggest a significant downgrading of the UK's nuclear deterrent, including the possibility of locking the warheads "in a cupboard" for delayed launch only after several weeks of mounting international tension.
A significant downgrade to the long-term forecast in next month's budget is now inevitable.
It would be a significant downgrade from an iPhone 6, isn't a quantum leap over the iPhone 5S and should only really be considered if size is the overriding factor.
George Osborne has placed a tax on sugary drinks at the centre of his budget, as he sought to mask a significant downgrade to Britain's economic potential with a flurry of initiatives and giveaways to small businesses, motorists and savers.
Compared to traditional watches, which smartwatches are attempting to replace, the chunky profiles and lack of premium fit and finish of last years' models made them a significant downgrade in personal style.
"But whilst we welcome the decision to keep the A&E open, Jeremy Hunt's failure to prioritise turning the hospital around in recent years has led to the loss of maternity and paediatric services at Stafford, representing a significant downgrade of the hospital".
