KCG Holdings, which has reportedly been strained by internal concerns over its recent performance, reported a loss in the most recent quarter as slower retail trading activity weighed on results.

"A number of factors coalesced to pressure revenues and revenue capture in US equities during the quarter," chief executive Daniel Coleman said in a release. "The seasonally slow July and August were followed by an active yet challenging September. The elevated levels of price improvement put added pressure on revenue capture."