Sinclair, currently on loan from Peterborough, will spend the rest of the season at the Keepmoat but has only managed 92 minutes of football since his arrival on January 4.
However Flynn has reassured the 25-year-old that he will get his chance and has warned he must be ready to take it.
"We've had numerous chats with Emile," Flynn told the The Star. "It's difficult for him to have come in at the time he did because the team have been winning.
"That's made it very difficult for him to break into the side. My advice for Emile is when the opportunity comes for him to take it.
"He will certainly have a big role to play between now and the end of the season. I say to players that every game is 14 v 14 because you have the opportunity to play three substitutes."