PARIS, Aug 31 (Reuters) - Credit rating agency Standard & Poor's (S&P) said on Thursday it had cut its rating on debt-ridden French supermarket retailer Casino down to "D" denoting a likely default, after Casino failed to pay the interest on a bond.

"Casino Guichard Perrachon S.A. has failed to pay the interest on its 400 million euros ($434 million), 2026 unsecured bond, due mid-July 2023, within the 30-day grace period stated in the original debt documentation," wrote S&P.

"Consequently, we expect Casino will fail to pay all or substantially all its debt obligations as they come due, and a general default to be a virtual certainty. We therefore lowered all our issuer credit and issue ratings on Casino and its debt to 'D' (default)," added S&P.

In July, Casino agreed upon a long-awaited debt restructuring deal with creditors led by Czech billionaire Daniel Kretinsky to avert bankruptcy. ($1 = 0.9223 euro) (Reporting by Sudip Kar-Gupta in Paris Editing by Matthew Lewis)