Visualise one in game taken out (7)
I believe the answer is:
imagine
'visualise' is the definition.
(I've seen this before)
'one in game taken out' is the wordplay.
'one' becomes 'i' (Roman numeral).
'taken out' is an anagram indicator.
'in'+'game'='ingame'
'ingame' anagrammed gives 'magine'.
'i'+'magine'='IMAGINE'
(Other definitions for imagine that I've seen before include "Reckon" , "Conjure up in mind,fancy" , "Picture to oneself" , "Form a mental image in the mind" , "Devise" .)