Composer, European, as is possibly accepted by fellows (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

E (abbreviation for European) + anagram (possibly) of AS IS , contained in (accepted by) MEN (fellows). Olivier Messiaen, 20th-century French composer and organist. After getting the first couple of crossers, I tried and discarded both Mascagni and Massenet before eventually finding him.