Tosun is a Turkey international, but the decision by Ozil and Gundogan - Germany internationals of Turkish descent - to meet the controversial leader brought condemnation from their football association (DFB), fans and politicians in Germany.
Several politicians condemned the pair’s decision to pose alongside Erdogan, whose regime has been condemned by human rights campaigners due to its arresting of journalists and opposition politicians, particularly in advance of elections in Turkey which Erdogan won in late June.
The Arsenal playmaker was booed during a pre-tournament friendly, and headed to the World Cup with the storm still raging. Germany's group-stage exit exacerbated the criticism, and Ozil was dropped for Die Mannschaft's sole win in Russia.
Following the World Cup, Ozil's father Mustafa advised his son to retire from international duty after being "offended" by the treatment he has received.
Ozil has been quiet over the matter during pre-season, but released an open letter via his Twitter account entitled 'Meeting President Erdogan' on Sunday morning.
The past couple of weeks have given me time to reflect, and time to think over the events of the last few months. Consequently, I want to share my thoughts and feelings about what has happened. pic.twitter.com/WpWrlHxx74— Mesut Özil (@MesutOzil1088) July 22, 2018
The message read: "The past couple of weeks have given me time to reflect, and time to think over the events of the last few months. Consequently, I want to share my thoughts and feelings about what has happened.
"Like many people, my ancestry traces back to more than one country. Whilst I grew up in Germany, my family background has its roots firmly based in Turkey. I have two hearts, one German and one Turkish. During my childhood, my mother taught me to always be respectful and to never forget where I came from, and these are still values that I think about to this day.
"In May, I met President Erdogan in London, during a charitable and educational events. We first met in 2010 after he and Angela Merkel watched the Germany vs. Turkey match together in Berlin.
"Since then, our paths have crossed a lot of times around the globe. I'm aware that the picture of us caused a huge response in the German media, and whilst some people may accuse me of lying or being deceitful, the picture we took had no political intentions.
"As I said, my mother has never let me lose sight of my ancestry, heritage and family traditions. For me, having a picture with President Erdogan wasn't about politics or election, it was about me respecting the highest office of my family's country.
"My job is a football player and not a politician, and our meeting was not an endorsement of any policies. In fact, we spoke about the same topic that we do every time we have met - football - as he too was a player in his youth.
"Although the German media have portrayed something different, the truth is that not meeting with the President would have been disrespecting the roots of my ancestors, who I know would be proud of where I am today. For me, it didn't matter who was President, it mattered that it was the President
"Having respect for a political office is a view that I'm sure both the Queen and Prime Minister Theresa May share when they too hosted Erdogan in London. Whether it had been the Turkish or the German President, my actions would've been no different.
"I get that this may be hard to understand, as in most cultures the political leader cannot be thought of as being separate from the person.
"But in this case, it is different. Whatever the outcome would've been in this previous election, or the election before that, I would still have taken the picture."