(Reuters) – Jamie Selway, the leading candidate to head the U.S. Securities and Exchange Commission’s Division of Trading and Markets, has withdrawn his name from consideration, according to a person with direct knowledge of the matter.

The Trading and Markets job is one of the last major positions new SEC Chairman Jay Clayton still has to fill. The unit oversees securities exchanges and markets, broker-dealers, clearing agencies, derivatives and the Financial Industry Regulatory Authority.

Selway, head of execution services at agency brokerage Investment Technology Group Inc, made the decision more than four months after his name was floated as the front runner for the position. The reason for the delay was not clear.

Selway was not immediately available for comment.

A widely respected expert on equity market structure, Selway co-founded institutional agency broker White Cap Trading in 2003 and was on the board of exchange operator Bats, which is now owned by CBOE Holdings, from 2008 to 2015.

Selway’s withdrawal was first reported by the Wall Street Journal.