CHELSEA manager Graham Potter said it was a "tough decision" to leave Pierre-Emerick Aubameyang out of their Champions League squad for the knockout stages but said the Gabon striker still has a role to play at the London club. Aubameyang was absent from the 25-player list named on Friday and there was no place for 35-million-pound ($42-million) January signing Benoit Badiashile, but British record transfer Enzo Fernandez was included. Mykhailo Mudryk, who joined for an initial fee of 70 million euros ($76 million) from Shakhtar Donetsk, and loan signing Joao Felix were also included in the list. "Pierre's a professional…