Valdes landed awkwardly when making a save from a routine free-kick during the first half of Barca's 3-0 Liga win over Celta Vigo on Wednesday.
The 32-year-old has since been diagnosed with a tear of the anterior cruciate ligament in his right knee, an injury that ends his hopes of competing in the FIFA World Cup in June.
The news also marks a sad end to Valdes' Barca career, having previously revealed that he will leave when his contract expires at the end of the season.
Javier Mascherano posted: "Nothing to celebrate. Get well soon @1victorvaldes."
Cesc Fabregas: "Good win but sad about @1victorvaldes's injury. Hope you recover soon. We are all with you!"
Jose Pinto: "Very sad for what happened with my teammate and friend @1victorvaldes I hope with all my heart that it's not really bad.
Spain team-mate Pepe Reina: "Sad news! Lots of strength to my friend @1victorvaldes! You'll soon be giving goalkeeping lessons again, genius."
