Credit ratings agency Standard & Poor's (S&P) has placed Syngenta on negative watch, following the Swiss pesticide and seed giant's acceptance of a $43bn (£29.7bn) bid from China state-owned firm ChemChina.
S&P said it's placed Syngenta's "A+" long-term credit rating and "A-1" short-term credit rating on negative watch, saying they could be lowered if and when the deal with ChemChina closes.
"While the company has announced that there is committed financing for the transaction, details are unavailable at this stage. Additionally, the degree of the Chinese government's potential support is also unclear," it said.
"If and when the transaction closes as planned, our view of ChemChina's credit quality, its financial policies, the future leverage of Syngenta, and its status within ChemChina will be key factors in our rating assessment."
The deal is expected to complete by the end of this year, subject to regulatory approval and a thumbs up from 67 per cent of Syngenta's shareholders.
And providing it goes through, it will be the largest ever overseas acquisition by a Chinese firm, and the second largest in the chemicals industry within the past year.
The new bid comes in the wake of Syngenta's rejection of a $46bn cash-and-stock takeover offer from rival Monsanto last year.