"significantly deteriorate" is a correct and usable phrase in written English.
You can use it when referring to a noticeable decrease in something. For example, "The economic outlook has significantly deteriorated over the last year."
The deterioration of the physical role was significant while physical functioning did not significantly deteriorate, which may indicate that patients perceived a decline in their physical conditions.
Analysts expect that area to significantly deteriorate as the economy plunges into a recession.
Many of those currently chortling away could find their personal circumstances significantly deteriorate as a result of decisions taken by the politicians they support.
If they are wrong, and the modest pace of economic growth slows or mortgage markets significantly deteriorate, "a few members" of the Federal Open Market Committee believe that "more policy stimulus" may be desirable, the Fed minutes said.
Missing on-going scanning activity can significantly deteriorate network performance.
Such a situation would significantly deteriorate the tsunami-forecast capability using ship data.
Consequently, discarding these couplings/correlations between agents can significantly deteriorate the localization performance and integrity.
'Nevertheless, amid this market chatter, our liquidity position in the last 24 hours had significantly deteriorated.
Bear Stearns had insisted for days that its finances were in adequate shape, but its chief executive said that the bank's liquidity had "significantly deteriorated" since Thursday.
McCluskey's relationship with Labour MPs who back Smith for the leadership has significantly deteriorated in recent weeks, including with his former flatmate Tom Watson.
His health "significantly deteriorated in last two months and he spent most of that time in the hospital where he died", the agency said.
