Chris Killen has reached an understanding with Ricki Herbert, the New Zealand manager, that his drive to become established at Celtic will not be interrupted by frequent demands to play for his country.

Killen, signed on a Bosman transfer from Hibernian, is in the final stages of recovery from a snapped Achilles tendon sustained in January and expects to be fully fit within two weeks.

Celtic's pre-season schedule begins in earnest on Monday when they fly out to Switzerland, yet Killen worked on his conditioning even throughout the brief two-week break he enjoyed in Crete. Impressing Gordon Strachan is currently the greatest priority for the 25-year-old, who has scored 15 times in 26 international appearances.

New Zealand's World Cup qualifying campaign begins in October, almost three years before the finals in South Africa. Those matches will be preceded by at least two friendlies, but Killen has been told he will be used sparingly to allow him to settle in Glasgow.

"New Zealand have got a little bit coming up and I spoke to my national team manager when they played Wales recently," said Killen, who helped launch Celtic's new away kit yesterday.

"I said I had to get myself fit and going at Celtic before I think about jet-setting off back to New Zealand for a couple of games.

"The manager knows my fitness is my priority and I want to play for my club as much as my country. I'm not writing anything off, but he knows that I need to get myself established here.

"There are a couple of qualifying games in the autumn and we'll probably be in contact again then. I don't imagine the manager is going to put pressure on me to fly 26 hours back home for any friendlies. To do that and then try and come back for a weekend match in Scotland is almost impossible.

"The manager understands that and is willing to let me miss them if it means playing in the bigger games when the overseas players are needed."

Killen could be ready for some on-field involvement when Celtic head for a tour of the United States later next month. He will be part of the group travelling to Switzerland next week but will not feature in any matches.

"I've only had two weeks off and have been working even when I was away," said Killen. "I missed the last four months of last season and have a lot of catching up to do. It's something I was more than willing to get on with because I want to be ready for the new campaign.

"I've had no reaction to the injury, it's just been a slow process. I've been trying to do as much as I can without setting myself back.

"I'm still a couple of weeks off from being fully fit. The physio wants me to take care over the next wee while so I won't be able to play in Switzerland. I'm looking to go out there with the boys, though, to train and work with them."

Celtic have already spent £8m so far this summer and are continuing to seek further additions before the new season commences.

Scott Brown has been the most expensive to date at £4.4m, and Killen is delighted to continue the association formed at Easter Road.

"Everyone knows how good Scott is and it will be great to play alongside him again," said the striker. "He'll be a great asset and I think that he can improve at Celtic. He'll put in the extra work to do that, as I will.

"I think I heard Scott before I ever saw him at Hibs. He's got a lot of mouth, as you all know, but he's got the quality to back it up. He's just a great guy to have around.

"He has tremendous enthusiasm and when things weren't going well he would do something to lift the boys. He is one of those players who can dig you out of the s**t and that's a great attribute for anyone to have. He plays to win no matter the opposition."