Gerard Pique said Barcelona missed Lionel Messi after they were beaten 2-1 by Sevilla in La Liga on Saturday.
The forward is out of action for eight weeks with a knee injury sustained in the victory over Las Palmas and the Catalans lacked a cutting edge in attack in his absence.
Goals from Michael Krohn-Dehli and Iborra gave the home side a 2-0 lead, before Neymar pulled a goal back as Barca laid siege to the Sevilla goal.
Neymar, Luis Suarez and Sandro all hit the crossbar but as they tried in vain find an equaliser and Pique admitted his side felt the loss of Messi and Andres Iniesta.
"After the international break, we must start winning and cannot afford more setbacks. Barcelona have to be at the top," he said.
"Of course we miss Messi and Iniesta, but Sevilla also have injuries so that cannot be an excuse.
"The ball didn't want to go in today. They got through twice and scored, we paid for that."
The defeat at Sanchez Pijuan is Barcelona's second in three league outings, but Suarez believes the latest loss differed greatly from their 4-1 collapse at Celta Vigo last Wednesday.
"Against Celta we didn't play well, but today we feel like we did everything we could," the striker said. "We deserved at least one point."