Mertens is struggling to earn a start in coach Rafa Benitez's team this season.
"The important thing is to give 100 per cent to help the team," Mertens insisted.
"I like to play from the start, like everyone else, and if I have to play for just half an hour then I'll do my best.
"The Coach decides when you play, and you have to accept that. Before the red card [on Monday] I played six minutes, but the important thing is winning."