Slew left Sheffield United with a warning from manager Danny Wilson that he will struggle to make it at Rovers.
"I definitely believe I can be a Premier League player. If I didn’t, I wouldn’t have come here," he said.
"I’m high on confidence right now, I feel good and I feel I’ve got a good chance of playing.
"I want to fight for a first team spot. All I can do is keep working hard in games and training, and score goals in matches, and hopefully the gaffer can see that and put me in."