Part of a shirt (6)
'part of a shirt' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sleeve that I've seen before include "Container for LP" , "Part of a shirt or jacket" , "Part of a shirt - old record holder" , "Covering for arm or sleeve" , "Possibly hiding-place for ace" .)
(Other definitions for collar that I've seen before include "Grab one" , "Part of a garment around the neck" , "Arrest (sl.)" , "Grab by the neckband?" , "Be hot under the . . . . . . to be angry or resentful" .)