Casoni replaced the sacked Sylvain Ripoll recently but the new manager quickly found out the enormity of the task ahead after his side lost 3-0 to title-chasing Monaco in his first game in charge.
Les Merlus have endured a nightmare season so far and they are sitting bottom of Ligue 1, losing 10 of their 13 matches which has left the club five points from safety.
Next up is an away trip to Metz, who are 12th in the table, on Saturday and Casoni believes his side need to start fresh if they are going to pull themselves out of their current predicament.
"We need to get back to basics, learn to walk again before we start to run," Casoni said. "This team has been conceding two goals a game for a year and a half now. We let in three against Monaco from eight chances. We need to get our defensive solidity back.
"Of course we still want to play good football but we mustn't forget to put on the safety catch. I want to use experienced guys to get us moving. The youngsters are still learning but I will watch them and they will get their chance."