Chelsea have nabbed their first transfer deal of the January window - securing the signature of USA and Borussia Dortmund winger Christian Pulisic for £65million.
Pulisic, 20, will stay with the German side until the end of the season.
He said: "In the summer I move to Chelsea and to a new competition, the English Premier League.
"It’s a privilege to have signed for such a legendary club and I look forward to working hard towards being a contributor to their team of world class players."
Chelsea director Marina Granovskaia said: "We are delighted to have signed one of Europe’s most sought-after young players. Christian has shown his quality during a fantastic spell in Germany and at just 20, we believe he has the potential to become an important Chelsea player for many years to come. We look forward to welcoming him to Stamford Bridge in the summer and wish him and Dortmund every success for the remainder of the season."
The future of Eden Hazard and Willian will be under greater scrutiny now with Hazard keen on a move to Real Madrid, while Brazilian Willian was a long-term target for Manchester United when Jose Mourinho was at the helm there.
Cesc Fabregas is expected to sign a pre-agreement with Monaco and will sign for the French side in the summer.