The flyhalf missed the 27-22 loss to Scotland in the opening round last weekend because of a calf injury but was given an outside chance of facing Italy.
Italy captain Sergio Parisse thinks whether Ireland have Best or not Italy will need another "miracle" on a par with November's triumph over South Africa to win.
"I think Conor got a good look at how we train and what we try to do".
Donnacha Ryan was fit to return at lock for Iain Henderson, and Jack McGrath's shaky start at loosehead prop saw him switched out for the man he ousted two years ago, Cian Healy.
Scotland led 21-8 before Ireland mounted a comeback.
However the well has since run dry, and since Italy moved to the Stadio Olimpico in 2012 Ireland have averaged a try a match, with a 50 per cent winning record. One of the biggest offenders was captain Sergio Parisse.
Duke-UNC basketball preview
Duke has won four of the last five in the series, but the two have split at the betting window in their last 10 meetings. Carolina is huge up front with Isaiah Hicks (12.8, 5.6), Kennedy Meeks (12.6, 9.4) and Justin Jackson (18.6, 4.8).
'We clearly didn't do that on a number of occasions and that's something that as a coach I'm certainly disappointed with, but the players were also disappointed with a few things that we didn't get quite right'.
Named Glasgow Warriors' Player of the Season past year, Simone Favaro's return is a huge boost for Italy for the remainder of the Championship. It's the country where I grew up and where I always wanted to play.
O'Shea, who played 35 times for Ireland, has made only four changes for Saturday as he seeks "consistency" while promoting internal competition.
"From a player's point of view, you don't want your captain not to be there for your captain's run, ideally", said Jamie Heaslip after the session.
After last week's late arrival at Murrayfield and subsequent slow start, Ireland will, of course, be hoping that preparations go off as planned tomorrow and they then begin well against the Azzurri.
Andries van Schalkwyk was named in the second row and will partner Marco Fuser instead of George Biagi, who has been dropped to the bench and the vastly experienced Leonardo Ghiraldini will start at hooker.