The 25-year-old - who has suffered from a hamstring injury ever since being withdrawn after 25 minutes of Ireland's opening RBS Six Nations win over Italy last month - failed in his bid to make the French game, despite an hour-long outing for Leinster last Sunday.
However, with that crucial "5% still missing" because of his injury, O'Sullivan feels "it's not looking good" for last season's player of the tournament.
"I don't think Gordon is going to make the Wales match the way things are going. There has been uncertainty over his injury for the last few weeks and it's not looking good," conceded O'Sullivan.
His progress has been monitored and will be re-assessed ahead of Tuesday's team announcement for the Millennium Stadium meeting with Mike Ruddock's Wales.
Ulster's Kevin Maggs proved an able deputy for the injured Leinster duo on Saturday - but the 68-cap centre will have been disappointed to not have had a bigger impact.