Doctor manic 'cos he’s put his foot in it? (8)
I believe the answer is:
moccasin
'he's put his foot in it?' is the definition.
(type of shoe)
'doctor manic 'cos' is the wordplay.
'doctor' indicates anagramming the letters.
'manic'+'cos'='maniccos'
'maniccos' is an anagram of 'MOCCASIN'.
(Other definitions for moccasin that I've seen before include "Put one's foot in it" , "Crow's foot perhaps covered in this" , "Soft leather 11" , "Soft shoe - venomous American pit viper" , "Soft, slip-on shoe - snake" .)