Reports in the British press suggest the Chelsea winger will pen an initial loan deal at Stadio Artemio Franchi.
The Germany international signed a five-year contract at Stamford Bridge in 2012, but has failed to gain regular first-team action at the Premier League club.
He spent the 2013-14 campaign on loan at La Liga outfit Sevilla, winning the UEFA Europa League.
It now appears the former Werder Bremen man will link up with Vincenzo Montella's side.
"Pending official [confirmation], Marko Marin is conducting medical visits," read a message on Fiorentina's official Twitter account, accompanied by a picture of Marin undergoing tests.
Marin made 18 appearances in Spain's top flight last season, but missed part of the campaign with a thigh complaint.
