Nothing being in touch is concerning (5)
I believe the answer is:
about
'is concerning' is the definition.
(about can mean concerning or relating to)
'nothing being in touch' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'being in' is an insertion indicator.
'touch' becomes 'abut' (abutting is a kind of touching).
'o' placed inside 'abut' is 'ABOUT'.
(Other definitions for about that I've seen before include "Apropos, concerning" , "Almost; around" , "Circa" , "Nearly" , "in the offing?" .)