The visiting Serie A outfit beat the Royal Blues 3-0. Gianluca Scamacca, Lazar Samardzic, and Nikola Krstovic scored for Atalanta.
Kolasinac, a Bosnia international, came through Schalke's Knappenschmiede academy after joining in 2011 and helped the Under-19 side secure the Bundesliga title in the 2011-12 campaign. He subsequently made his senior debut against Greuther Furth in September 2012.
Kolasinac established himself as a first-choice left-back between 2012 and 2017, accumulating 141 competitive appearances and scoring five goals.
His standout 2016-17 season brought three Bundesliga goals and five assists, earning him a place in the division's Team of the Season.
He departed for Arsenal on a free transfer that summer before briefly returning to Schalke in January 2021. The defender was handed the captaincy immediately and featured 17 times in the Bundesliga during a difficult 2020-21 campaign.
"I was really excited to get to play at the VELTINS-Arena again. Even though I'm no longer part of the Royal Blues, I still consider myself a Schalker! That's why it was a really special day for me.
"It was an incredible moment, one that I will enjoy looking back on.
He added: "I could feel the excitement rising over the last few days. I spoke several times with Edin (Dzeko) and Nikola (Katic) and they texted that they were feeling the same way."
