United have yet to win any of their 12 matches under manager Micky Adams and are second from bottom in the table, six points adrift of safety, but Ertl - who escaped relegation with Crystal Palace last season after a last-day win at Sheffield Wednesday - has not thrown in the towel.
The Austrian said: "If you're committed to the club and the cause and wear the badge with pride, you can stay in this league.
That's what we have to do now. Everyone has to stick together. "If anyone drops their head and says `this isn't going to work out' - that's just rubbish in my opinion.
"So many people are writing us off but there are still plenty of games left and there's still hope. We have to stay positive and encourage each other because things are getting better."
Ertl added: "It's a tough league but I think we're going to make it. The team spirit is great despite our situation in the table. We have to show mental strength and toughness now but we can make it because everyone is going in the same way and we are committed."