New Rovers boss Dickov has turned to the vastly-experienced 64-year-old to be his right-hand man upon the club's return to the Championship.
Horton, who has also managed Oxford, Huddersfield, Brighton, Port Vale and Macclesfield, told Rovers' official website: "It's brilliant to be here. It's a great club with a fantastic training ground and stadium and with promotion to the Championship last season I'm really looking forward to it.
"I know Paul through the Manchester City connections and when we spoke he said he wanted some experience with him and that is why I decided to come - it's great to be back in football.
"This is my 49th pre-season and when you're not in the game you miss it so it is great to be here with this set of players and staff."