An officer drove by the victim as he was lying on southbound Tomball Parkway near North Gessner just before 5am.
The officer said he thought the man may have been intoxicated, but then noticed he had actually been struck in an apparent hit-and-run.
The man was still breathing. He was taken to Ben Taub General Hospital in serious condition, officials said.
The southbound lanes of Tomball Parkway were blocked while police investigated and cleared the scene.
There were some car parts in the roadway that may be from the vehicle that hit him, but no other evidence was gathered and there are no witnesses in this case. If you have information, call police or Crime Stoppers.