Dieng, who has signed a four-year contract, won the Africa Cup of Nations with his national side in 2021.

The Swiss-born keeper has flown to the Algarve to join Boro's training camp, with their opening Championship fixture against Millwall on 5 August.

Dieng strengthens manager Michael Carrick's goalkeeping department after the departure of Zack Steffen, who returned to Manchester City after a season-long loan.

The club have also signed goalkeeper Tom Glover and outfield players Morgan Rogers, Sam Silvera, Alex Gilbert and Rav van den Berg.

Dieng had 12 months left on his QPR contract after making 120 appearances for the Loftus Road club, and joins a Boro side which reached the play-offs last season before losing to Coventry.

He signed for the London club after spells at Swiss clubs Grasshoppers and Red Star Zurich led to a short stay with Duisburg in Germany, and then two appearances for non-league AFC Fylde on a trial basis.