“Lately we haven't played our best football. After a year of doing so well, it's a more difficult moment and we want to get back to our level as soon as possible," Mertens told Mediaset Premium.
“It was a tough game today, plus we heard the news from elsewhere. We must immediately return to Naples and get ready for the next match so we can get back on track.
“It's not just me, but the whole squad that is in a difficult moment. We've got to raise the tempo and that will make our style of football work much better.
“We have to focus on ourselves and how we can all do better. We mustn't forget the talent in this side and we had the chances to make it 2-0 here, but didn't take them.
“Obviously, there is disappointment, but we mustn't forget how well we were playing and realise we can get back to that very soon."