Gayle moved to Selhurst Park from Peterborough United in July 2013 and has scored six goals in 13 appearances across all competitions for the club this season.
However, the 25-year-old striker has found himself on the periphery of the first team since Warnock returned as manager in August.
The 66-year-old stated that he was unhappy with Gayle's showing when he came off the bench in Saturday's 1-1 Premier League draw with Stoke City.
And with Warnock openly admitting he is searching for a new striker in the January transfer window, Gayle has been given an ultimatum to improve in order to fight for his Palace future.
"He [Gayle] hasn't pushed himself into pole position in training really," Warnock said.
"I was disappointed when he came on against Stoke if I'm honest. And in training he's not really knocked my door down.
"It's like Wilfried [Zaha] earlier on [this season]: they've got to show me what they can do in training, to get back in the team.
"At the moment, the lads who are in the team have got the shirts really, and it's up to others to knock the door down, saying 'I'm doing this well, I should be back in the team', which is not happening."
