Central defender Vitorino Hilton has signed a one-year contract extension with Montpellier.
AC Milan have completed the permanent signing of defender Cristian Zapata from Villarreal for an undisclosed fee.
Hancox, who has agreed an initial six-month deal, predominantly plays full-back but can be utilised on the wing.
The youngster joined the club aged eight and started alongside Nathan Redmond, who regularly featured in the first team last season.
"It's an amazing feeling to sign your first pro contract with the club you support," Hancox told the club's official website.
"I need to go into pre-season flying and try and get in front and then take it into the early part of the season.
"As long as I have a good start I don't see why I can't get another deal but I'll have to wait and see."