"I'm very excited and happy to be at Chelsea and I'm looking forward to next season," said Nusken, who has won 15 caps and scored twice for Germany.

"It's a big club with such good players and I hope to improve my football skills."

Nusken, who has scored 12 times for Frankfurt during her three years with the club, added: "I wanted to move to the Women's Super League because it's a good league, English football is very cool to play in and it's the right thing to do now."

Chelsea boss Emma Hayes added: "Sjoeke is a fantastic young midfield player whose ability to play the ball deep into the opponent's half is not her only standout strength, there is everything from her interceptions, her reading of the game and her overall presence.

"She's dynamic, she's good aerially and she's going to be a fantastic signing for this club."

Chelsea are a point behind WSL leaders Manchester United but play their game in hand against West Ham on Wednesday for a chance to re-gain the top spot with two matches remaining.