The 23-year-old joined United from the Cumbrian outfit in 2011 when he was just 14-years-old.
The Sun says each time Henderson plays, the League Two outfit pick up £10,000 on the back of the deal they made with United when he was 14.
Until this season, the goalkeeper had not made a senior appearance for the club.
Carlisle did not receive any funds for appearances he made while he was away on loan.
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