"We lost decisive players," admits Mertesacker to the Mail on Sunday. "And Robin started so well at United. We asked each other, "How can he behave like that and hurt us like that?" Because he scored decisive goals, right from the start.
"We spoke a lot of times about it when we travelled away and they (United) scored. It was like, 'Another one! Another decisive one!' But then you imagine that it's our chance to show that he's not responsible for whole team; that he's gone now and he has another target with United.
"Straightaway our thoughts were, 'We have to deal with it'. We knew over the whole of last season he had rescued us a lot of times, scored a lot of goals at the end of the games, a lot of free-kicks.
"I think we replaced them (Barcelona's Song and Van Persie) well in terms of scoring goals. It's not only one player but three or four players who have scored 10 goals on average this season. What will be vital is to keep all the players that grew over the last year and learned a lot playing together. It could be vital to keep all of them - and maybe get some new players in."