The Scottish international has been dropped a number of times this season for summer signings Daniel Cousin, Jean-Claude Darcheville and Steven Naismith.
The striker has also been linked with a move to Birmingham but this was strongly denied by the player.
"I read the stories about Birmingham and it was an obvious assumption to make. Alex signed me for Rangers and we did well for each other.
"He also picked me regularly for Scotland so I knew there would be speculation when he got a new job.
"But leaving Ibrox has never entered my mind. I want to stay at Rangers, get back in the team, score goals and win trophies.
"There's nothing else in my head. I still feel I have to prove to the fans I deserve to wear the no.9 - that's my sole aim."