McIlroy's inauspicious start to 2013 continued with a disappointing tie for 41st in the US Open this month. He is yet to win this year, has been headed as the world No1 by Tiger Woods and shown signs of frustration following his lucrative switch to Nike clubs.
Yet as he and McIlroy prepare to compete in front of home crowds at the Irish Open, McGinley has defended the double major winner's inconsistency.
"My opinion on Rory six months ago is the same opinion I have now," McGinley said. "I don't think Rory is ever going to be a flat-line golfer. I think it's in his DNA to be up and down.
"If you look at him this time last year, the same questions were coming; why has Rory gone off form, he missed three or four cuts in a row, he's this and that. Then all of a sudden after a few weeks off he wins the US PGA Championship and he played fantastically well.
"He is never going to be a Nick Faldo who is going to flat line. We just have to accept that and let him get on with it. He will come through the bit of a trough that he has had; he'll come through and have success again. I don't see Rory as a flat-line player and I just think that's going to be part of his career for the rest of his life.
"Everybody is different and one of the reasons why he is so exciting is the fact that he is up and down. That's one of the reasons why Seve was so exciting, he was up and down, too. I think that's the X factor that Rory has. He can win every week."
Padraig Harrington said: "Rory is only ever one golf shot away from playing great."
McGinley also believes Justin Rose's US Open victory, his first major success, offers a boost to those looking to make up the European Ryder Cup team at Gleneagles next year. Rose was the first English player in 43 years to claim the US Open.
"If you look at things historically and not just for European players, when someone breaks through and wins often their peers step up to the plate after that," McGinley added.
"So I would not be surprised to see a number of English players, particularly, stepping up now and performing at the Open Championship and USPGA. I think it can only be a good thing because people will think : 'If Justin can do it, I can do it.' So I am looking forward to the reaction of the European players who think Justin has broken the mould, let's go and follow him."
The Royal and Ancient has dismissed a report that the Open Championship will return to Royal Portrush in 2018 or 2019. The Northern Ireland venue remains under consideration but concerns over logistics and infrastructure mean another Irish Open, possibly in 2015, is likely to be held before a decision is made regarding the third major of the season. Portrush hosted the Irish Open last year.
"The R&A continues to examine the possibility of the Open returning to Royal Portrush. However, reports that The Open is to return there later this decade are without foundation," a spokesman said.
At present Open venues up to and including Royal Troon in 2016 have been confirmed.
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