Masters' shirt seams partly turned back (7)
I believe the answer is:
Here is my best explanation:
'masters' shirt seams partly turned back' is the definition.
I can't judge whether this defines the answer.
'shirt seams partly turned back' is the wordplay.
'partly' says the answer is hidden in the clue.
'turned back' says the letters should be written in reverse.
'irtseam' can be found hidden inside 'shirt seams'.
'irtseam' in reverse letter order is 'MAESTRI'.