The Clarets, who face Arsenal on Sunday in the fifth round of the FA Cup, are seventh in the Championship having already reached the semi-finals of the Carling Cup.
That has meant a total of 47 matches so far this season and even if they lost at the Emirates Stadium Burnley would still have at least another eight games to play - with more if they qualify for the play-offs.
Veteran defender Graham Alexander, 37, has played every match this season plus four for Scotland and compatriot McDonald said he was an example to all the squad.
"We've played 47 games and we have still got a few left but the fitness levels here are great and we can't let it get to us," said the 20-year-old.
"The players that have played have done so well to keep us where we are in the cup and the league.
"Graham Alexander is 37 and he has played every game - that's unbelievable.
"If I'm still playing at 37 I'll be very surprised. The experienced players help us through and it makes us a decent team.
"The amount of games we have played is noticeable but it shows you the fitness levels of the boys.
"Everyone gets tired but I think it is mostly in your head but the cup run helps."
Burnley have already beaten Arsenal once this season, with McDonald scoring both goals in the 2-0 Carling Cup quarter-final victory in December.
However, he is expecting a much different proposition tomorrow having beaten a side made up of mostly reserves at Turf Moor nearly three months ago.
"It is a much different game. If Arsenal put out their top stars they can beat most teams in the world so it is going to be hard," added the former Dundee midfielder.
"Not many Premier League teams or teams in the Champions League would expect to go there and win.
"It is going to be hard on the day. We will just stick to our task."
Burnley have, this season, beaten Premier League clubs Chelsea, Fulham, West Brom and Tottenham in cup ties and McDonald said that would help the players as they look to book a place in the FA Cup quarter-finals.
"It has given us some respect and the games we have played have boosted our confidence beating those teams," he added.
"I've never been to the Emirates Stadium but it looks amazing on the television. Hopefully it will be full on Sunday."