Celtic face the first leg of their qualifier in mid-August and the Australian knows they have to be in top shape to make the group stages.

McDonald expects to return to Glasgow feeling the benefit of their games against the MLS All-Stars and Chicago Fire.

He said: "It's great to come to places like America, experience different types of games and play in different climates.

"The quality of the opposition is really high as well, and that can only help for the start of the season when the competitive matches begin.

"When we get back, there are only a few weeks before we have the qualifier for the Champions League. That's massive for the club.

"Financially it's vital, and for all the players it's a massive thing because we want to play at the highest level in Europe and help bring success to the club."

McDonald came to Britain as a teenager with Southampton before signing for Motherwell.

But the 23-year-old keeps in touch with the A-League back in his native country and he feels the American public are taking to football in a similar way to the Australians.

The arrival of David Beckham at LA Galaxy last week has boosted the profile of Major League Soccer around the world and in the US itself.

"The signing of David Beckham has given the MLS a lot of publicity, but I think most people know there are quality players in this country," said £700,000 summer signing McDonald.

"In terms of the MLS, it's a case of onwards and upwards from here. It's pretty similar to back home in Australia.

"Soccer is not the major sport there, but you can see the popularity rising. America is much the same and that's good."