Placed a cover outside (4)
I believe the answer is:
laid
'placed' is the definition.
(laying is a kind of placing)
'a cover outside' is the wordplay.
'cover' becomes 'lid' (lid is a kind of cover**).
'outside' indicates putting letters inside.
'a' put within 'lid' is 'LAID'.
(Other definitions for laid that I've seen before include "Doze" , "(Of dining table) set" , "Put down like dial" , "tables may be?" , "Wagered" .)