O'Driscoll was a spectator as France defeated Ireland at Croke Park

O'Driscoll was a spectator as Ireland's Grand Slam ambitions were left in tatters, but he should be fit for the game against England on 24 February.

"I knew no matter how well we prepared, there wouldn't be that edge to our attack and defence," said O'Sullivan.

"There's no point saying that we don't miss him."

Extended highlights: Ireland 17-20 France

O'Sullivan added that his side had been without "the best international centre in the world, and that's no reflection on Shane Horgan".

"I don't think any country in the world could replace Brian O'Driscoll if they had to. It did hurt us not having him and it was tough leaving him out."

Despite O'Driscoll's absence, O'Sullivan was impressed with France's strength and expects them to defend their Six Nations title.

Even so, the Irish coach believes a coveted clean sweep of victories is becoming increasingly unlikely as the tournament continues to improve across the board.

"France can complete the Grand Slam every year. They are always up there because they have a phenomenal squad," he said.

"But they went to Scotland last season and were beaten against the odds and only won the championship over us on points difference.

"We're only two games into the Six Nations. Most wise people would predict there will be very few Grand Slams won in the current era because it's so tight.