Leicester Tigers prop Michele Rizzo will miss Italy's final game of the Rugby World Cup after picking up a knee injury in their 16-9 defeat to Ireland on Sunday.Rizzo, a try-scorer in Italy's win over Canada earlier in the competition, is one of three players to withdraw from the Azzurri squad. Former Tigers prop Martin Castrogiovanni is to have treatment after scans found a tumour in his back, while centre Gonzalo Garcia also has a knee injury.   Benetton Treviso's Alberto De Marchi, capped 28 times, and Zebre's uncapped Andrea Lovotti have been called up as replacements for Rizzo and Castrogiovanni.   Italy face Romania in Exeter on Sunday in their final Group D fixture needing a victory to secure third place and automatic qualification for the 2019 Rugby World Cup.