Warnock, 34, looks to have played his last game for the Rams after joining Wigan Athletic on loan until the summer, when the former England international will be out of contract.
Wassall has failed to include Warnock in any of his last four matchday squads, having named him on the bench for his first game in charge - last month's home defeat to Milton Keynes Dons.
But Warnock's lack of action will come as no surprise to the player himself.
"When I first took over, I told Stephen that Marcus Olsson was going to be first choice (left-back)," Wassall said, as quoted by the Derby Telegraph.
"I said we'd love him to stay and fight for his place but we also understand that he is out of contract in the summer and would be looking for another club for next season.
"So, we didn't want to stand in his way.
"He has been a great pro while he has been with us and played very well for the first team on numerous occasions this season.
"But we think it is right and proper that we help him try to get a new club for next season.
"He told me he wanted first-team football. I couldn't guarantee that. Hopefully, he will do well for Wigan."
Warnock, who only arrived at the iPro Stadium in January 2015, has played 22 times for Derby this season and captained them on occasion.
The Rams, who are without fellow left-back Craig Forsyth with a long-term knee injury, can recall Warnock after 28 days should anything happen to Olsson in the meantime.
Warnock is the second experienced head to be shown the door by Wassall, after Chris Baird, who rejoined Fulham on loan last month.