Former Ireland international Shane Horgan has backed Simon Zebo to be a success at fullback if Rob Kearney does not recover from injury in time for the Pool D clash with Italy on Sunday.

Speaking to RTÉ Sport's Game On, the former Leinster man said that if Kearney is ruled out due to a glute injury he suffered in the 44-10 win over Romania, Zebo can slot in "seamlessly at 15".

"All of a sudden Rob is a doubt, he’s strained his glute, I'm not certain if that is something that will clear up in a week," said Horgan.

Horgan feels that if Kearney, who should know the extent of the injury soon, does not recover then Zebo can continue his good form.

"Zebo was very impressive at the weekend.

"He was getting on the ball a lot, his passing was excellent, distribution very good, variety of passes very good. He was attacking players at every opportunity and he was looking really quick and sharp.

"There are fewer concerns over his catching game, which has improved steadily over the last six months, and his positioning on the field.

"If there is a problem with Rob then Zebo will slot in fairly seamlessly at 15."

There is also competition for places on the wings after the Irish side ran in 13 tries in their opening two games, although Horgan believes only one spot is up for grabs.

"I think Dave Kearney is nailed down to start. I think Tommy Bowe did have a good game yesterday but may have not shown enough form thus far to take over

"If Zebo is not an option at wing and he is at fullback [instead of Rob Kearney], then we are looking at Luke Fitzgerald, who has impressed and is a [Joe] Schmidt favourite, or Keith Earls, who has just been exceptional over the last couple of games and was rightly man of the match.

"Earls seems to have an incredible knack for scoring tries now – Ireland’s leading try scorer in the World Cup ever.  He’s bringng great form and looks very quick.

"Earls may start if [Rob] Henshaw is not ready at 13."

Competition for places is not limited to the backs, as Horgan pointed to Joe Schmidt's second-row selection headache, with Paul O'Connell, Devin Toner and Iain Henderson competing for two jerseys

"We haven't seen the last of Toner either. There's been a huge push for Henderson to start in the second row along with Paul O'Connell, but I think we saw Toner really fighting for his position [against Romania].

"He was good at the set pieces and carried the ball well, he's well able to distribute the ball. I think that’s going to be a very tight call."

Rob Henshaw and Kearney are the only injury concerns ahead of the clash with Italy in London, and Horgan expects Ireland to deliver more of the same on Sunday.

"What's really encouraging for Ireland is that we don’t have to get hung up on what our first 15 is" - Shane Horgan

"Everyone's had a run out, Henshaw aside, everyone will be confident and you have to expect whatever team he puts out against Italy will be more than enough for them."

Horgan said that while he didn't want to write off the Azzuri, he expects Ireland to win.

"You don't want to diminish any World Cup game because there's a certain pressure that comes with it that you'll only find in a World Cup, but Italy haven't played well in a long time.

"They haven't brought any form into the World Cup, they haven't shown any form and I think Ireland are playing a couple of levels above Italy."

Even if Sergio Parisse does make his expected return to face Ireland, Horgan does not expect Ireland to struggle.

"I know they've been missing Parisse, the party line is that he is the talisman, but he is but one man and our back row is very physical, it's very strong.

"[Chris] Henry had a great performance yesterday and he's ready to slot back in.

"What's really encouraging for Ireland is that we don’t have to get hung up on what our first 15 is.

"Almost right across the squad there are a huge amount of players that can slot in or slot out and that is increasingly going to become more important."

The schedule, which sees Ireland face the two weakest teams in the group in the earlier matches has also worked in our favour, Horgan believes.

"We're so lucky that we've had the opportunity to play against teams where there hasn't been the same impactful, physical nature of the game and we're a little bit battle-hardened after two games.

"The Italian game will be a step up but we seem to be very sharp from our rolling plays, we seem to be trying a lot of things from set plays to break teams down directly from that and I think those things bode really well for Ireland and could cause Italy huge problems."