CRAIG GORDON insists he has not joined Celtic to replace Fraser Forster, or Lukasz Zaluska - but to challenge them.

More importantly for the man who has been out of football for more than two years, he wants to challenge himself.

The 31-year-old admitted he could have accepted the knee injury - which has forced him under the knife twice - had brought a premature end to his playing career.

Having played in England's top flight, become the most expensive goalie in Britain when he moved from Hearts to Sunderland for £9million in 2007, and won 40 caps in an illustrious spell as Scotland's undisputed No.1, he was entitled to be content with what he had achieved.

He could simply have picked up the sizeable insurance pay-off he was due and settled into media work.

But Gordon did not want to run the risk of sitting back in later life asking himself - what if?

Now he is delighted his dedication and determination have earned him a two-year deal with the SPFL champions.

Today he begins training with his new team-mates at their Austrian training camp, and he is eagerly anticipating the battle between him, Forster and Zaluska beginning.

He said: "I haven't asked for any guarantees, and I didn't expect any.

"It has been down to me in the last two years to get myself back to this position.

"Now it is down to me to force myself into getting a game here.

"Who knows what the future holds? I don't.

"I am of the mindset that Fraser and Lukasz are going to be here, and I will fight them for a place.

"If they are not here, I will fight whoever comes in.

"I don't know what will happen with regards to that. I just know I'll battle my corner to try and get a game."

There is obvious and understandable relief that Gordon has finally got himself back into the game.

He forced himself through months of pain after surgery to repair the tear in the ligament attached to his knee cap.

Through his former goalie coach at Hearts, Jim Stewart, Rangers offered him training facilities and physio.

And tentative discussions over joining the Ibrox club had begun.

But, when Celtic invited him to train with them at the end of last season, he jumped at the chance.

The two main stumbling blocks regarding a contract were the condition of his knee, and the fact Neil Lennon quit to be replaced by Ronny Deila.

It took four weeks of talking then an intensive medical to seal the deal, and he admitted: "When there was a change of manager, I didn't know what would happen.

"But, I've spoken to [goalie coach] Stevie Woods and the new manager, and they were keen to get it done as soon as possible so I could get out to Austria with them.

"The medical was very strenuous, over a number of days, focusing on everything, not just my knee.

"It was tough, but it was a good few days, and it's nice to know what the knee is capable of, because you get pushed to the limits.

"It was good to come through that."

Now the target is winning a starting place with Celtic, then regaining his Scotland spot.

Gordon has no intention of believing the job is done just because he has defied the sceptics to win a contract.

He has already shown he is made of much more than that by refusing to let the curtain come down on his career, with a healthy compo cheque to keep his spirits up.

"I could have done that, but didn't want to do that," he said emphatically.

"I'm a footballer, and that means going out there and challenging yourself.

"There's no challenge in sitting back accepting money for doing nothing and spending the rest of your life wondering 'what if?'

"Playing football is what has driven me on to keep trying and what's got me to this point."