The 26-year-old only joined Palace last summer, but he failed to make an impact in his first season at Selhurst Park and only made three starts, which all came in the final three games of the season.
With several clubs thought to be interested in the Austrian, Warnock intimated that he would be keen to get him off the wage bill, but he now looks to have had a change of heart.
"Ertl has done alright in the final three games," Warnock told the Croydon Advertiser.
"He is desperate to stay at the club, he has a tremendous work ethic and I've been happy with him over the last few weeks.
"It's not absolutely urgent that we sell him in the summer - we are just looking at ways we can save money."