Kagawa signed for the current champions when he was 21 from Japanese side Cerezo Osaka and his progress has been slow but steady with the striker making an impact in the second half of the season having scored nine goals from 16 starts.
The 23-year-old hinted recently that he would be interested in a move to the Premier League and Dortmund sporting director Michael Zorc admitted earlier this month that "the ball is in his court".
The youngster is quick on his feet and likes to utilise a burst of pace to make space for himself before lashing the ball into the net. Chelsea are keen to bring a player of his calibre as they believe he would fit in well with their brand of direct attacking football.
AC Milan are also said to be interested in the midfielder who would also boost their popularity in the Japanese market much like the manner of how Park Ji Sung has done for Manchester United in Korea.
But general manager Hans-Joachim Watzke stated recently that the club are planning to open negotiations over a new long-term deal and wish to tie down the midfielder at the club.
"I think he will still be playing at Dortmund beyond the end of next season, but you can never be sure," Watzke was reported as saying according to talkSPORT.
"We want to keep him and extend his contract.
"He wants to go to England? I don't know, but I keep hearing things in the press."
Kagawa was signed for €350,000 but he will likely make a handsome profit for the Borussians as Chelsea will have to fork out a figure of nearly €15 million to bring him to Stamford Bridge.