interim boss Rafa Benitez.
Sources close to the deal believe the 22-year-old attacking midfielder, capped 22 times by Germany, will join next month.
With Atletico Madrid striker Radamel Falcao also expected to move to Stamford Bridge - despite reports of a link with Manchester United last week - in a £45m move, Chelsea are ready for another big spending summer.
Their transfer strategy is still being run by technical director Michael Emenalo, with the club also looking for a holding midfielder and a No 2 goalkeeper to replace Ross Turnbull.
Belgian stopper Thibaut Courtois is rated highly by the club but will spend another season on loan at Atletico Madrid.
With Benitez having already admitted he will leave the club in the summer, regardless of whether he lands an FA Cup and Europa League double, Everton boss David Moyes, former Chelsea manager Jose Mourinho and Manuel Pellegrini, currently at Malaga, are all being considered.