Chelsea are watching Bayer Leverkusen midfielder Hakan Calhanoglu.
The Daily Mail says Chelsea sent scouts to watch Bayer at Cologne last week with attacking midfielder Calhanoglu a player under scrutiny.
Arsenal, Tottenham, Manchester United and Everton were also represented at the game.
Bayer Leverkusen's 20-year-old German international Julian Brandt also of interest.