Canada's main stock index lagged at open on Thursday, hurt by losses in materials and financials stocks as risk appetite remained on a weak footing a day after a surprise downgrade of the United States' credit rating.

At 9:30 a.m. ET (1330 GMT), the Toronto Stock Exchange's S&P/TSX composite index was down 91.8 points, or 0.45%, at 20,126.41.

(Reporting by Siddarth S in Bengaluru; Editing by Milla Nissi)