Chelsea have announced the signing of the forward Christopher Nkunku from RB Leipzig on a six-year contract. The deal has been in place for months and the 25-year-old has become the club’s first signing since Mauricio Pochettino took over as manager. Chelsea have paid close to €60m (£51m).

Nkunku, who can play in a number of positions across the front line, underwent medical checks with Chelsea at the end of last summer’s transfer window. The France international scored 23 goals in 36 games for Leipzig this season, including three in seven Champions League appearances.

“I am incredibly happy to be joining Chelsea,” Nkunku told the club’s website. “A big effort was made to bring me to the club and I am looking forward to meeting my new coach and teammates and showing the Chelsea supporters what I can do on the pitch.”

Chelsea are poised for a busy window, with three of their outcasts – Édouard Mendy, Kalidou Koulibaly and Hakim Ziyech – closing in on lucrative moves to clubs in Saudi Arabia.

They are expected to raise further funds by selling Mason Mount to Manchester United, Mateo Kovacic to Manchester City and Kai Havertz to Arsenal. Chelsea are set to step up efforts to sign the Brighton midfielder Moisés Caicedo and the Villarreal striker Nicolas Jackson. Well-placed sources believe they will bid for the Celta Vigo midfielder Gabri Veiga soon.