Knight Capital Group Inc. KCG +36.30% confirmed that the embattled brokerage had agreed to a $400 million rescue plan that would help fill a hole left by errant trading last week.

The Jersey City, N.J.-based firm told regulators in a filing Monday that the firm had entered into a "securities purchase agreement" on Aug. 6, selling $400 million worth of 2% convertible preferred stock in itself to a group of investors. Those securities will be convertible into about 267 million shares of common stock in the company at about $1.50 a share. Knight currently has about 89 million shares outstanding.

The deal was anticipated to be "consummated" Monday, according to the filing from Knight.