Mats Henrik Berne Wieffer (born 16 November 1999) is a Dutch professional footballer who plays as a defensive midfielder for Premier League club Brighton & Hove Albion and the Netherlands national team.

[8] He made his debut for Excelsior on 29 August 2020, replacing Mitchell van Rooijen in a 1–6 win against Jong PSV in the Eerste Divisie.

[9] On 29 May 2022, he scored in the penalty shoot-out as Excelsior beat ADO Den Haag in the final of the play-offs to promote to the Eredivisie In June 2022, Wieffer moved to Feyenoord on a four-year contract.

[10] After getting injured in a friendly against Red Bull Salzburg in pre-season,[11] he made his debut for Feyenoord and in European football on 8 September 2022, coming on as a substitute for Javairô Dilrosun in a 4–2 defeat against Lazio in the UEFA Europa League.

[15] He assisted goals of Oussama Idrissi and Igor Paixão on 14 May 2023 as Feyenoord beat Go Ahead Eagles 3–0 to secure its sixteenth Eredivisie title.

[20] He made his Premier League debut in Brighton's opening match against Everton on 17 August 2024, where he'd register an assist as the Seagulls would go on to win 3-0.

[21] On 17 March 2023, Wieffer received his first call-up to the Netherlands senior national team for the Euro 2024 qualifying matches against France and Gibraltar.