On 16 July 2017, Cengiz Ünder became a Roma player for a €13.4 million fee. He scored his first goal for Roma in a 1–0 win over Hellas Verona in the Serie A on 4 February 2018. In the same month, he marked his Champions League debut with a goal; the opener in a 1–2 loss to Shakhtar Donetsk in the first leg of the first round of knockout fixtures, becoming the youngest Turkish player ever to score in the Champions League. Following the Afrin offensive in Northern Syria, which was carried out by the Turkish Armed Forces in January 2018, on 11 February, Ünder performed a military salute as a goal celebration after netting in Roma’s 5–2 home win over Benevento in Serie A. In October 2019, following the Turkish offensive into north-eastern Syria, Ünder posted a picture of the aforementioned celebration on Twitter; his controversial post drew criticism on social media from Roma fans.