"To lose Lionel Messi means football loses and we lose," said Barca boss Luis Enrique.
Messi limped off just before the hour mark of the Spanish champions' 1-1 draw with Atletico Madrid on Wednesday.
The Argentine captain is set to miss his country's World Cup qualifiers against Peru and Paraguay next month as well as Barca's Champions League clash at Borussia Monchengladbach.
Messi will also sit on the Catalans' La Liga trips to Sporting Gijon and Celta Vigo.
However, Messi should be fit in time for a reunion with old boss Pep Guardiola when Manchester City visit the Camp Nou on Champions League duty on October 19.
Messi ready but won't be risked: Luis Enrique
The five-time World Player of the Year missed Argentina's World Cup qualifier with Venezuela earlier this month due to the problem and only started Barca's shock 2-1 defeat to Alaves 10 days ago on the bench as coach Luis Enrique bedded him back into action gently.
"Now we have to look for other solutions," said Enrique. "With Leo we are much stronger, but without him we are still a strong team."
Barca coped remarkably well with eight wins from 10 games when Messi was sidelined by a hamstring injury for two months last season.
And Enrique hopes his side can show similar resilience to avoid slipping further behind Real Madrid in the title race.
"Last year we had an unfortunate situation with a longer-term injury and my team played well," he said.
Barca remain three points behind Madrid at the top of La Liga after Angel Correa's equaliser seconds after Messi limped off handed Atletico a share of the spoils at the Camp Nou.
Atletico's Torres relishing clash against Barcelona
Ivan Rakitic headed Barca into the lead just before half-time, but Atletico marshalled Messi's star strike partners Luis Suarez and Neymar well in his absence to hold out for a point.
Suarez, though, insisted he and the Brazilian can step up as they did without Messi last season.
"It is a difficult injury that hurts and leaves you sad," said Suarez. "Now we have to take responsibility."
Suarez was involved in a battle of his own as he was booked for a clash with Atletico left-back Filipe Luis six minutes from time.
Luis posted a photo of a stud mark piercing his bleeding foot on his official Instagram page after the match with the message: "Just as well he didn't touch me."
However, Suarez lambasted Luis for not reacting likewise when he was sent-off for a brutal challenge on Messi when the sides clashed back in January.
"This is football, it is a man's game and what happens on the pitch stays on the pitch," added Suarez.
"You can't make a show of things every time something happens. Last year he didn't post a picture of Messi. I repeat, football is for men."
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