Fletcher recently joined Wednesday in the summer transfer window following his release from Premier League club Sunderland at the end of the 2015-16 season.
The 29-year-old striker plays with Bannan for the Scotland national team, and he has revealed the discussion he had with the 26-year-old midfielder before his move to the Owls.
“I did speak to Baz [Bannan] before I came down and he gave me a little heads up over what it would be like,” Fletcher told The Star.
“I had already made my mind up by then but I just spoke to Baz. He’s full of banter. We just had a laugh.”
“He’s a great talent and he showed that last year by how well he did,” added Fletcher. “He has said it himself that he wants to maintain that form this season.
“Every time we have played together at international level with Scotland, we have linked up well so hopefully we can take that understanding into this season.”
Fletcher scored four goals and created eight chances in 16 Premier League appearances for Sunderland last season before joining Marseille on loan in the January transfer window.
The 29-year-old former Hibernian and Wolverhampton Wanderers striker scored two goals and created 16 chances in 12 Ligue 1 matches for Marseille.
Bannan scored two goals and created 58 chances in 37 Championship appearances for Wednesday during the 2015-16 campaign.
The former Aston Villa and Crystal Palace midfielder had a pass accuracy of 81% and a shot accuracy of 31%, and won three headers, 27 dribbles and 45 tackles.