NMC - which recently revised its debt position to $6.6 billion, well above earlier estimates - has seen its stock more than halve in value since December after short-seller Muddy Waters questioned its financial statements.
Dubai Islamic Bank said on Sunday it has a $425 million exposure to NMC Heath, while its subsidiary Noor Bank has a further $116 million.
The aggregate exposure to NMC constitutes approximately 0.7% of DIB's total assets as of March 31, the bank said.
Shares in DIB were down 4.8% in afternoon trade after the disclosure, underperforming the Dubai stock index, which was down about 2.2%.
Emirates NBD, Dubai's biggest bank, said it had an exposure of 747.3 million dirhams ($203.5 million), including 676.5 million linked to its unit Emirates Islamic Bank.
The latest revelations came after Abu Dhabi Commercial Bank, which has a $981 million exposure to NMC Health, said on Saturday it had asked a court in Britain to put the company into administration to safeguard its future.
That process would give the healthcare group, whose London-listed shares were suspended in February, protection from creditors, and avert a more disruptive liquidation.
NMC Health's new executive chairman on the same day called on the company's creditors to suspend debt repayments and said he would work with authorities in Britain and the United Arab Emirates (UAE) to recover misused funds.
Shares of ADCB were trading 3.1% lower in afternoon trade.
Other banks also made disclosures at the request of bourse operators in the UAE.
Abu Dhabi Islamic Bank said it had extended $291.4 million in financing to NMC Healthcare LLC UAE, guaranteed by NMC Health, and that it had an additional $31 million exposure to Islamic bonds issued by NMC.
National Bank of Fujairah pegged its exposure to NMC at 289.1 million dirhams, while Sharjah-based United Arab Bank said its exposure was 135.3 million dirhams.
ADIB shares were down 4.9% on Sunday.
Marie Salem, head of institutions at Daman Securities, said banks will have the opportunity to assess their exposure to NMC Health by June and take any action, such as writedowns, if necessary.
DIB said it was now in discussions with NMC and its advisors to ascertain the group's financial position and identify potential measures to address its governance and financial issues.
By Saeed Azhar