VfB Stuttgart left-back Cristian Molinaro was also brought back into the squad for the Euro 2012 qualifiers against Northern Ireland and Serbia after Luca Antonelli withdrew.
Gilardino and Antonelli were named on Sunday but after checks at Italy's Coverciano base it was decided they would not recover from calf and foot problems in time for Friday's match in Belfast or the October 12 clash in Genoa against the Serbs.
"Alberto Gilardino and Luca Antonelli are going home. Sergio Floccari and Cristian Molinaro are arriving," a federation statement said.
Coach Cesare Prandelli, whose side top Group C after two wins out of two, has been operating with three up front but said he could consider playing two forwards in the coming matches given a lack of wide options.
Manchester City's Mario Balotelli, earmarked as a wideman in a front three, is out for several more weeks after knee surgery.
"I don't have a lot of forwards who can play wide. I want to put the opposition under pressure and a diamond midfield could be an alternative," Prandelli told a news conference.
The coach said Fiorentina midfielder Riccardo Montolivo, a member of the ill-fated World Cup team in June, had been left out of Sunday's squad because of an ankle complaint and had not been overlooked.
Floccari's selection, which follows Lazio's surprise surge to the top of Serie A, is a huge snub to dropped Juventus World Cup duo Vincenzo Iaquinta and Fabio Quagliarella.
