Haynes has been with the club since 2012 when spotted at a youth tournament in Rugby.
The youngster made his professional debut in 2013, playing the whole game in a 1-1 draw against Bradford. He made two further appearances in the season, both ending in draws against Shrewsbury Town and Crawley Town, respectively.
Now seen as a regular within the first-team set-up, the 20-year-old scored his first professional goal in the 3-2 win over Peterborough in 2014 and joined Cambridge United on loan at the backend of last term, making 10 appearances.
Haynes started and scored in Coventry’s 3-2 EFL Cup win over Portsmouth this season to help the Sky Blues advance to round two in the competition.