Fletcher has not played for Scotland since suffering an ankle injury early in the 2-1 World Cup qualifying defeat by Wales on March 22 but is back in the squad for Friday's friendly against the United States after recovering from a dislocated shoulder.
Bannan said: "He's a massive player. He has scored goals at the top level in that league and to see him back in the squad has given everyone a boost because he has that presence that he is going to score a goal for you so it's brilliant to have him back."
However, Scotland have won their last two games with Steven Naismith up front and previously won in Croatia when Gordon Strachan started with Leigh Griffiths, who did not make the squad for the games against the USA and Norway.
And Bannan knows Fletcher will not take anything for granted in the face of competition.
"People see him in the team sheet and they start to fear him because he has scored goals at the top level," Bannan said.
"But the boys that have been here when Steven was injured have been brilliant. Naisy and Leigh Griffiths have been brilliant so it's going to be hard for Fletch to get in because there is competition for places."