Ireland winger Keith Earls is convinced the celebrated Test career of Brian O'Driscoll could extend until the 2015 World Cup.

O'Driscoll will win his 123rd cap for Ireland in Sunday's RBS 6 Nations clash with Scotland at Murrayfield. But his future, beyond participating in a fourth Lions tour this summer, remains undecided.

The 34-year-old centre was man of the match in the championship opener against Wales and impressed against England a week later, suggesting he still has plenty to offer at the highest level.

Staying fit remains his greatest challenge, however, after successfully returning from surgery on the trapped nerve in his neck that dogged him throughout the 2011 World Cup and an ankle operation in the last two years alone.

But Earls has seen enough to believe that O'Driscoll could defy his own expectations and make the next World Cup in England in 2015.

"Brian was amazing against Wales - I couldn't believe it," said the Munster back, who will be making his first start of this year's Six Nations in place of the injured Simon Zebo.

"The surgery on his neck has given him massive relief and you can see that in his body shape.

"Now he's able to do weights, something he wasn't able to do for a couple of years. It's made a massive difference to him.

"I wouldn't be surprised if he goes on until the next World Cup - he's feeling fresh and is buzzing.

"You get goose bumps when you're watching the video back of him play because in my eyes he's one of the best rugby players to have ever walked on a pitch.

"I wouldn't be surprised if he goes on until the next World Cup - he's feeling fresh and is buzzing" - Keith Earls.

"He has no fear, but is also very intelligent in the way he thinks about the game.

"His presence lifts you because you know he's willing to do anything for you and the team. It makes you want to do the same for him."

Earls may only be 25-years-old, but alongside O'Driscoll and Rob Kearney, 26, he views himself as one of the elder statesmen of a backline than has undergone a youthful overhaul since the autumn.

Scrum-half Conor Murray is 23, while fly-half Paddy Jackson, inside centre Luke Marshall and right wing Craig Gilroy are 21. Jackson and Marshall will be making their Test debuts on Sunday.

"Brian, Rob and myself are the oldest now - it's a bit weird all right being only 25 but one of the oldest," Earls said.

"It's exciting times now, though not so good for me being one of the old lads!

"It's great to see young lads coming through. The future's really bright and everyone's buzzing.

"The young fellas are keeping us on our toes and bringing a fearless attitude into the game, which is great.

"The squad has changed a lot since I first came in. Before the team never changed much."

Ireland enter a pivotal match in their Six Nations knowing that victory would propel them back into the title mix while defeat would further deflate a championship that started so brightly in Cardiff.

Adding to the size of the stakes at Murrayfield is that coach Declan Kidney's chances of extending his contract until the next World Cup would be dealt a potentially mortal blow if Scotland win.

The tactics used in the 12-6 defeat by England were puzzling with the Irish failing to bring their greater experience to bear, but the error count was huge and Earls insists that for this only the players are to blame.

"If the players aren't performing it's put on his (Kidney's) head, but we're all in it together," he said.

"We're really positive. We had a great win against Wales and lots of errors against England.

"Having got back to 6-6 it was very frustrating. When we did the review we saw we had 30 turnovers while England had 10.

"We'll stick at it and play for each other. All games now are make or break.

"We've got a tough test ahead of us. Scotland are on a high and are performing well. They have a few new faces so are playing positive rugby.

"The championship is definitely there to be won as there are a lot of big games left to play. It's still wide open."