 Pröpper made 4 appearances in the 2017–18 FA Cup including the 2–0 quarter final defeat away to Manchester United.On 7 April 2018, Pröpper was shown a straight red card for a late challenge on Jonathan Hogg in a 1–1 home draw against Huddersfield Town.On 4 May, Brighton were to face Manchester United again, this time in the league where Brighton won 1–0 at Falmer Stadium securing Premier League status.