Rossi underwent a medical in Florence Saturday morning before signing a contract sealing a transfer from Villarreal to the Serie A club prior to the visit of Pescara.
Fiorentina's fans will have to wait a while yet before seeing him in action though, as the serious knee injury which he picked up last April - and which ruled him out of Euro 2012 - still needs a few more months to heal.
Keeping his place warm will be Stevan Jovetic and Rodrigo Gonzalez, whose goals have taken Fiorentina into contention for a place in the Champions League next season.
Both were on target in a 3-0 win over Palermo which saw the Viola end 2012 in style, and in third place.
That has set the bar high for 2013, but coach Vincenzo Montella is keen to keep it that way.
"Our aim is to give it our best all the time and to try to remain at these levels," he told Sky television.
"We started from scratch in the summer, wanting to relaunch this side."
Opponents Pescara also started afresh in the summer following their promotion to Serie A, and the defections of coach Zdenek Zeman and key players Lorenzo Insigne, Ciro Immobile and Marco Verratti.
They turned the page again just before Christmas with the appointment of Cristiano Bergodi as their new coach, and after a 2-1 win over Catania, he is confident the Abruzzans can avoid the drop.
"I believe we can stay up and I believe in the potential of this side," he said.
"We are happy. Everybody has got to give their own small contribution to the cause for us to stay up."
Pescara go into the last game of the first half of the season two points above the relegation zone.