A top Sydney lawyer will fight allegations that he grabbed the groin of a young woman as she jogged on a beachside track in northern Sydney.

Carl Harrap, a senior lawyer with the law firm FPA Patent Attorneys, pleaded not guilty to one count of indecent assault in Manly Local Court on Wednesday morning.

Mr Harrap, 40, is accused of grabbing the 20-year-old woman's vagina from behind in Clontarf between 8.45am and 9.11am on December 28.

In court documents, police allege that the offence was of a "sexual nature" and Mr Harrap did not know the woman.