Thompson will replace Chris Paterson in the Edinburgh side after the stalwart injured his foot in their impressive win over Irish giants Leinster last Friday.
And Thompson admits he was preparing for a comeback game with draft club Heriot's, but insists he has no fears about being thrown in the deep end for the must-win clash in Italy.
He said: "I aimed to be back playing this weekend, but I wouldn't say I was expecting to be in the squad.
"I was looking at my draft club Heriot's playing away in Hawick so it was a nice surprise to be told I was in the starting line-up.
"There's not much difference really. Mansfield Park or Viadana? Probably be a similar pitch, similar weather and similar crowd.
"It's good being laid back and I am quite laid back about it. There's no point getting too worked-up about it.
"It was the same when I was on the bench with Scotland (in Argentina). You have to just treat it as another game and trust your ability."