Quagliarella suffered a season-ending injury on Thursday after tearing the anterior cruciate ligament in his right knee against Parma.
Marotta said: "It's a deal that started and concluded today.
"Toni has no need for a presentation. He reduced a part of his wages [to join the club].
"Toni doesn't arrive to replace Quagliarella but to reinforce an area of the team where there is need of him.
"He will already be available for the away match against Napoli on Sunday evening."