Arriving from Sheffield United in June 2016, the former Manchester United youngster went on to make 87 appearances in Green & White scoring 18 goals.
During 2017/18, Khan became the first Town player to score 10 goals before the turn of the year since Phil Jevons in 2004 before a stop-start second half to the campaign.
Commenting on the departure, Darren Way told YTFC.net: “Otis made a massive contribution with his goals and assists during his time with us and is a prime example of what you can achieve at this football club.
“We’ve built the club to a point where we don’t have to sell without remuneration and within two-years Otis has come in and moved on for a substantial sum.
“It’s four years since we last received a transfer fee and we now look forward to developing our next crop of talent whilst being in a position where we don’t have to sell.”