The 18-year-old has extended his deal, which was due to run out at the end of next season, until 2016.
Mensah has come through the Hornets' academy and has netted 12 goals in 14 appearances for the club's under-18 side this season.
View : 65251 times
View : 61129 times
View : 48135 times
View : 41876 times
View : 32919 times
Find detailed TV schedules for all Eurosport channel.
Find all the sports news on iPhone, BlackBerry, Android and iPad.
Follow up to the minute sports reports with Eurosport.