Fletcher has not featured for the national team since October 2012 after suffering from a chronic bowel condition known as ulcerative colitis, which required surgery.
The midfielder missed the majority of last season for Manchester United and has played just six times in 2013-14, with Bannan adamant that having Fletcher back has given everyone in the Scotland squad a huge lift.
"He's like the daddy of the team," the Crystal Palace midfielder told reporters as Scotland prepared to depart Glasgow airport for Wednesday's friendly in Poland.
"You look up to him because of what he has done and just to have him back is a big, big boost for the whole country.
"I was young when I first broke through and he was one I was kind of in awe of and looked up to.
"He made it so easy for me. It's good to have him back. He's the captain and the leader."
