Forced off in the first-half, Sissoko says he returned to the away dressing room after seeing Raheem Sterling score his goal - which VAR eventually overturned.
He revealed: "I did not even see that the goal had been canceled so in my head we were eliminated.
"One of the staff members came back to the locker room and told me it's amazing and we did it.
"I said, 'but how did we do it?' He told me that the goal was canceled. I forgot the injury, I ran away and it was an emotional shock."