The Australian signed a new five-year contract with the Clydesdale Bank Premier League champions yesterday after returning from a three-week spell on the other side of the globe playing in his country's World Cup qualifiers.

And he may further demonstrate his commitment to the Parkhead club by foregoing an extra break given to players involved in international duty.

McDonald, who scored 31 goals for Celtic following his £700,000 move from Motherwell last summer, said: "Coming back to the ground after three weeks away, I'm chewing at the bit again, albeit I need a bit of a rest.

"I've just finished with international duty, so I will get a couple of weeks away and refresh the body and the mind and come back as hungry as ever.

"I think everyone is back on July 4 but everyone who has been on international duty is allowed an extra break.

"I'm weighing it up at the moment and will see how I feel after the next couple of weeks, and see how refreshed I feel.

"If I feel good enough, I'll be back the same time as everyone else, because I don't really like missing out on anything.

"I like to know I've done the same as everyone else. It's what's best for me, and best for me would be to come back at the start of pre-season.

"I believe if you have a very good pre-season, it could make the difference for the rest of the season."

McDonald featured in two World Cup qualifiers against Iraq after helping his club pip Rangers to the SPL title.

"It's been a hell of a busy schedule but it's all done now," the 24-year-old said.

"I love playing for my country but this has been the longest season of my career.

"I've played 50-odd games and it's been quite a lot on the body. It's just good now to get a couple of weeks off.

"You can only get stronger week in, week out by playing. I've learned a lot over the course of the season.

"There were times when I felt tired in training but there are ways to make sure that doesn't happen again."

McDonald is the only man to sign on at Celtic so far this summer, while Rangers are set to complete the purchase of their third striker in a week with Kyle Lafferty following Kenny Miller and Andrius Velicka.

Celtic had made an offer for Lafferty but McDonald is unfazed by the reinforcements coming into Ibrox.

"I'm not really concerned with what's going on across the road," he said.

"They are all very good players, two of them are proven in the SPL, Kenny and Velicka, so they are going to improve Rangers' squad.

"But we are quite confident the squad we have here at the moment is good enough and will hopefully make if four (titles) in a row."