This from Sky Sports:
The Serie A outfit claimed at the start of the week that Vidic had signed a contract with them, with the intention of moving in January.
The Viola revealed they would take the case to Fifa and ask world football's governing body to rule on the issue.
However, Fiorentina have now decided against pursuing the matter and have confirmed they are closing the Vidic chapter.
"AC Fiorentina consider it is worth giving up trying to obtain the services of the footballer Nemanja Vidic after the recent events," read a statement on the club's official website.
"Considering the unreliable nature, and the evident unreliability of the player, we have decided not present anything to Fifa to safeguard our interests."
The Times:
Manchester United breathed a sigh of relief last night when Fiorentina dropped their complaint over the deal to sign Nemanja Vidic, but questions remain as to why the Barclays Premiership club agreed to pay £2.4 million more for the Serbia and Montenegro defender than appeared necessary under the terms of his contract with Spartak Moscow.
Vidic, 24, is expected in Manchester this week to discuss personal terms and undergo a medical examination before completing a £7.2 million transfer. It is a deal that has sparked anger in Florence, where Fiorentina believed they had secured an agreement to sign the player, but, after the Italian club decided against lodging a complaint with Fifa, the world governing body, the only remaining mystery surrounds the sums that United were prepared to pay — not only to Spartak but also to the player, who signed a £25,000-a-week contract to join Fiorentina on November 20, but will be offered around double that at Old Trafford.
United announced on Christmas Day that they had agreed "an undisclosed fee" to sign Vidic, but it has since emerged that the figure in question was €10.5 million (about £7.2 million). United could claim that sum is substantially less than the £11 million that Sergey Shavlo, the Russian club’s president, demanded when negotiations opened in mid-December, but it is also considerably more than they would have had to pay if the player had invoked a €7 million get-out clause in his contract.
There is no suggestion whatsoever of impropriety, merely that United appear to have been forced to pay over the odds as a result of an agreement between Spartak and Vidic. Spartak rejected a £4.8 million offer from Liverpool in November, saying that the clause could only be invoked at the express demand of the player rather than simply triggered by a bid from another club. This instantly aroused suspicions at the Merseyside club, who had previously been alerted to Vidic’s willingness to leave Moscow, which he stated in several interviews, most recently referring to his desire to join United.
As with the three other incoming deals completed since the club delisted after the takeover by the Glazer family in the summer, it is unlikely that the size of the fee, or indeed any payments to agents, will be made public if and when the deal is completed.