The Brazil international damaged the anterior crucial ligament in his left knee during Tuesday's 2-0 victory over Chelsea in the Carling Cup quarter-final at Stamford Bridge.
The 24-year-old was inundated with messages of goodwill on Twitter and he responded in kind.
"Just to confirm that I will be out until the rest of season," he wrote. "I am really sad with the news because I was enjoying [it] a lot on the pitch.
"I am sure I will come back stronger and I will achieve everything that I dream with the LFC shirt. I am sure I'll never walk alone."