The Guangzhou Evergrande playmaker was presented at Fiorentina on Monday, and he will play for the Stadio Artemio Franchi outfit until the end of the season.
Diamanti, who played for Fiorentina on loan in the 2002-03 season, could move to the club permanently ahead of the 2015-16 campaign, and is in line to play against Chievo on Sunday.
"When I heard Fiorentina were interested I didn't think twice about accepting their offer," he said. "I'm keen to get stuck into this new challenge.
"I'm happy and I can't wait to play. I feel at my best, all I need is matches to get back up to speed.
"I will get my head down and work as always. This is a major challenge for me. My career has been strange but I like challenges."
Fiorentina were not the only Italian side to make a loan acquisition on Monday, with strugglers Parma agreeing a deal for Andi Lila.
The midfielder – who has 51 caps for Albania – moves from PAS Giannina in Greece.
