Neagle's attorney, Harvey Steinberg, filed the plea on Tuesday in Jefferson County District Court. Neagle was not present.
Police issued the solicitation citation on Dec. 3 and the Rockies terminated Neagle's contract three days later under a personal conduct clause. The players association has challenged the termination.
Neagle, an oft-injured left-hander who has not pitched since July 2003, had been pulled over for speeding in the west Denver suburb of Lakewood. When an officer asked why Neagle's belt was unbuckled, a woman riding with Neagle said he had paid her $40 for sex.
The woman, Jill Russell of Denver, has been charged with prostitution.
Steinberg declined to comment Thursday and said Neagle would have no statement. Neagle's next court appearance was set for April 7.
Neagle was owed $19 million under his $51 million, five-year contract with the Rockies when he was released.
The Rockies cited section 7 (b) (1) of the Uniform Player Contract, which states the team can terminate the contract if a player shall "fail, refuse or neglect to conform his personal conduct to the standards of good citizenship and good sportsmanship or to keep himself in first-class physical condition."
The 36-year-old Neagle has had elbow ligament and shoulder surgery since last pitching. He has a 124-92 career record with a 4.24 ERA over 11 seasons, including 19-23 with a 5.57 ERA with the Rockies.
In 2003, Neagle was charged with drunken driving after he drove his sport utility vehicle into the back of another vehicle. He pleaded guilty.