[4] Dennis started the season on the bench mostly before being given his UEFA Europa League debut to Feyenoord on 3 November, which ended 1–1.

His performances attracted both Manchester City as well as an unknown Bundesliga side, who were interested in signing him in the winter transfer window.

Dennis started the season extremely well, scoring five goals in six matches, including one on his debut on 26 July 2017 to İstanbul Başakşehir, a 3–3 draw and a brace three days later in the league over Lokeren, which finished in a 4–0 victory.

On 1 October 2019, Dennis scored twice in a 2–2 draw at the Santiago Bernabéu Stadium against Real Madrid in the group stage of the 2019–20 UEFA Champions League season.

[17] On 13 August 2022, Dennis signed with Premier League side Nottingham Forest for an undisclosed transfer fee.

[24][25] Dennis was part of the Nigerian squad that lost on away goals with an aggregate score-line of 1–1 to the Black Stars of Ghana in the third round of the 2022 FIFA World Cup qualifying.