The former Werder Bremen centre-back says the time he had spent with the 25-year-old playmaker at the Bundesliga club meant he could be “honest” with his Germany team-mate
The 29-year-old centre-back was seen yelling at his compatriot when the former Real Madrid playmaker refused to applaud the travelling Gunners fans after the club's 6-3 loss to Manchester City at the Etihad Stadium.
But Mertesacker insists the pair have not fallen out over the altercation due to their long-standing friendship and believes such friction can be healthy.
“It can't just be all happiness, peace and pancakes,” the Germany international told Bild. “If it is, then you won't develop as a team.
“The good thing is that Mesut and I know each other well from our time at [Werder] Bremen. We can be honest with each other.”
The Gunners were handed a tough Champions League last-16 draw against reigning champions Bayern Munich, but Mertesacker believes the side can take heart from their victory at the Allianz Arena last season.
“It's a good draw,” continued the Arsenal centre-back. “I still remember how paralysed Bayern were when we made it 2-0 [last season]. We nearly toppled them then ...”