Teacher's account seen by the man as source of worry (8)
I believe the answer is:
headache
'source of worry' is the definition.
(I've seen this before)
'teacher's account seen by the man' is the wordplay.
'teacher' becomes 'head'.
'account' becomes 'ac'.
'seen by' means one lot of letters go next to another.
'the man' becomes 'he' (**).
'head'+'ac'+'he'='HEADACHE'
'as' acts as a link.
(Other definitions for headache that I've seen before include "Cause of worry or trouble" , "Severe problem" , "Problem, nuisance" , "Worry, trouble (colloq.)" , "trial" .)