Milan, who last season reached the round of 16, were placed in Group F, having won an appeal at the Court of Arbitration for Sport (CAS) to allow them to take part.
Bundesliga side RB Leipzig and Austrian outfit Salzburg, both closely identified with the Red Bull energy drink brand, will meet for the first time in competitive matches after being drawn in same group.
Leipzig and Salzburg were paired in Group B of Europe’s second-string club competition alongside Scottish champions Celtic and Norwegian side Trondheim.
Chelsea will also have some travelling to do after they drew Belarus side BATE Borisov, Hungarians Vidi and Greek side PAOK in Group L.