Chelsea need to avoid defeat to reach the knockout round.
Maresca said, "Tomorrow, we will do some rotation because the ones who played two games are quite tired to play again.
"So we will make rotation, and we will see if there is a chance for those who haven’t played as much."
On the Philadelphia heat, the manager also said: "It’s almost impossible to train a full session because of the weather.
"We are trying to save energy for the game; this morning’s session was very short, just plan for tomorrow, that’s it. No more than that.
"It’s not easy with these temperatures, but we will give our best tomorrow to get to the next stage of the competition."
Football can produce bad surprises
Maresca, warning of Tunis' quality, added: "Football is full of surprises – bad surprises – so we need to be ready for the game tomorrow and win the game.
"When you are the Chelsea manager or a Chelsea player, any game you don’t win is a headline.
"We are used to that. Tomorrow is a game where we have to do the right things to go through to the next stage and we will need to give our best."