The Argentina forward faces a spell on the sidelines after sustaining a groin injury in Wednesday's 1-1 La Liga draw with Atletico Madrid.
"There's no question we are stronger with Messi," Iniesta told Cadena Cope radio ahead of Saturday's match at Sporting Gijon. "When these things happen we all have to give a little bit more.
"We lost two points against Atletico and we have to make sure we don't throw away any more."
Third-placed Barca, who won eight of their 10 games when a knee injury kept Messi out for two months last season, are three points behind La Liga leaders Real Madrid.
Zinedine Zidane's Real, who missed out on a La Liga record 17th straight victory when they drew 1-1 with Villarreal on Wednesday, visit Las Palmas on Saturday.
Real talisman Cristiano Ronaldo failed to find the net against Villarreal but Zidane was unconcerned.
"I'm not worried if he doesn't score," said the French coach. "I'm worried when he isn't out on the pitch.
"What matters is for him to regain his form because he'll always get goals."
Las Palmas striker Kevin-Prince Boateng was sent off in a 4-1 defeat at Real Sociedad on Wednesday and is suspended.
Atletico host Deportivo La Coruna on Sunday and will be in positive mood following Angel Correa's second-half equaliser against Barca.
Second-placed Sevilla travel on Saturday to Athletic Bilbao who are riding a three-game winning streak in La Liga.
Unbeaten Sevilla, 1-0 winners over city rivals Real Betis on Tuesday, are two points behind Real Madrid after five matches.
(Writing by Adriana Garcia; Editing by Tony Jimenez)
