The Ghana international has twice ruptured his cruciate ligament and rumours surfaced that the 31-year-old had failed his medical ahead of his proposed transfer to the Italian club from Chelsea.
"Essien is fit, all the rumours about his fitness are just urban legends, I don't even know where they have come from,” Galliani told reporters. “I directly followed all the medicals and they assured me that there has never been any problem.
“We thought our squad was good enough, then we faced a problem concerning next Champions League game against Atletico Madrid. We won't be able to field both [Riccardo] Montolivo and [Sulley] Muntari, so we looked for a suitable replacement, and we agreed that Essien was the man.”
Transfer speculation has also linked Milan’s Kevin Constant with a move to Napoli, with Pablo Armero moving to the San Siro in exchange, but that switch now appears dead in the water.
“The Constant-Armero swap? Constant doesn't agree, so at the moment everything is on stand-by. Our transfer window is not closed yet.”
Meanwhile, Filippo Inzaghi will remain in his coaching role with the club until his contract expires, after reports linked the 40-year-old with a move to Sassuolo.
“Sassuolo wanted to sign Pippo Inzaghi as their new coach, but we didn't let him go. He has a deal until 2016 and he will stay with us for two more years. He understood the situation. "