Immobile had to be substituted after 29 minutes in the 0-0 draw against visiting Udinese in Serie A last Sunday after suffering a medium-grade injury to his left hamstring.
"The absence of players who have certain numbers is heavy, it happens to all those who have such impactful players. If Paris St Germain did not have (Kylian) Mbappe they would be a little worried, like Barcelona without Lewa (Robert Lewandowski)," Sarri said.
"We don’t have one (player) with similar characteristics, we have to go for different characteristics.
"The risk of losing some potential is there, we still managed to do well at the end last year. We have to give 100%."
Lazio have not given a timeline for Immobile's recovery but Gazzetta dello Sport reported earlier this week that he will be out until January 2023.
"We're making every attempt, I've seen that the guy is tough to want to shorten the time, it can be done and there’s no margin for risk," Sarri said.
Follow all the action from Serie A this weekend on Flashscore.
