Clifton recently had an operation on his knee, which is likely to keep him out for a lengthy spell.
He was unlikely to feature much in the Hawks’ plans so the club and player reached a settlement allowing him to leave.
‘After his operation it looks like Adrian is going to be out for a long time,’ said Hawks manager Lee Bradbury.
‘It would have been a waste of time dragging him up and down from London.
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‘It is a bit of a shame really.
‘Adrian is a good player but we didn’t see the best of him last season.’
Clifton arrived last summer from Maidenhead United with a reputation as a goalscoring attacking midfielder.
After a promising start, his goals and performances faded and he suffered from a number of injury problems.
At Maidenhead he was played just in behind the strikers and he always felt that to be his best position.
With the Hawks he found himself playing in a wider role and struggled to adapt.