The right-back remains suspended and under investigation by the FA, after he was suspended by AFC Bournemouth at the end of last season.
Jimenez's move to Italy was confirmed on the Serie A website on Monday, but it is understood that Bournemouth were waiting for international clearance before confirming the loan.
Read more:
The loan agreement includes a €20million option to buy plus bonuses, and the Cherries will get 30 per cent of a future sale from Fiorentina for the right-back.
Jimenez became a regular for Bournemouth last season, after he joined the club on loan from AC Milan in the summer.
(Image: Richard Crease)
That loan deal had an obligation to buy clause for if the right-back started, or played more than 45 minutes, in 50 per cent of Premier League games that he was available for, and the move was made permanent in February after he started against Aston Villa.
Bournemouth paid a fee of €19m for the right-back, with a further €5m in add-ons in the deal and Jimenez signed a five-year deal.
Milan were set to receive €5m plus 50 per cent of the rest of the money, with the other half going to Jimenez’s former club Real Madrid.
The Spaniard started all but one of the games after that, with one substitute appearance at Burnley, before he was suspended by the club with three games left to play in the season.
(Image: Richard Crease)
Social media posts involving Jimenez, but not posted by the Spaniard, were published in the week leading up to Bournemouth’s trip to Fulham, prompting a swift response from the club.
He was dropped from the team ahead of the game at Craven Cottage, and a Cherries statement said they "understood the seriousness" of the matter and it confirmed that an investigation was underway.
(Image: Richard Crease)
It is understood that this external investigation is still ongoing, and the club believes a move away is the best option for all parties involved, with Bournemouth holding a duty of care for Jimenez while awaiting a verdict in the investigation.
In total, Jimenez made 32 appearances in all competitions for the Cherries last season.
Thirty-one of those came in the Premier League and one in the FA Cup.
He scored once for the club, in the 3-2 win over Liverpool in January, and provided one assist, at Newcastle in the cup.
The 21-year-old returns to Serie A, where he is set to add to his 26 appearances in the Italian top flight with new club Fiorentina.