Cryptic

[1010k]

four letters, concerning which ??C?
Clue in place of singer dropping round? Not even sure of "C"! Thank you in advance! X

[davegosling]

Loco, maybe? In loco means "in place of", as in in loco parentis. Can't parse the rest, though.

[fiction-factory]

So are there two separate clues for this?
Or can I ignore the "concerning which " bit?

[davegosling]

I just assumed that the OP meant to write:

In place of singer dropping round? (4) ??C?

I may be mistaken.