Coutinho was one of Barca's top targets during the summer but saw three bids for the Brazilian turned down by Liverpool, who refused to sell despite the player handing in a transfer request.
Barca are expected to revive their interest once the window reopens next month, and Iniesta believes that the 25-year-old, along with Colombia international Yerry Mina, would be a good addition for Ernesto Valverde's side.
"I think they would be two important reinforcements to the squad," Iniesta told reporters.
"If the club wants to strengthen those positions, it should be with players that can be prepared to withstand the pressure of a club like this, and they would be two big signings. But nothing has happened, so it's difficult."
Barcelona currently sit five points clear at the top of the Liga table and eight above fourth-placed Real Madrid.