Masi was voted the player of the tournament in last year's RBS 6 Nations with his try-scoring performance against France helping the Azzurri to a 22-21 victory over their Gallic cousins for the first time in the Championship.
But Saturday's match saw Italy pull the scores level at 10-10 just before half-time only to concede four more tries as Ireland ran out convincing winners.
And after seeing the game get away from Italy, Masi is adamant fitness levels need to be increased in future if they are to get anything from their remaining games.
"In my opinion today we had physical drop off on the pitch," Masi, who has 67 caps to his name, told the Gazzetta Dello Sport.
"It wasn't concentration it just was physical, with 50 minutes gone we were the fresher but then Ireland were.
"However we've got to continue to play with the spirit we have because even against Ireland we had a positive spirit.
"We tried to play, yes we committed errors but I don't believe there are that many negatives."
And Masi knows things will have to get a lot better if they are to live with the Grand-Slam seeking Welsh at the Millennium Stadium in two weeks time.
"More or less I'm expecting Wales will be like Ireland.
"We will come up against a team that is really physical - more physical than we are.
"We must change our attitude and try to get better in that regard."