The stint starts with a trip to Perth to take on the Glory on Wednesday night.

United will then travel to Gosford to meet Central Coast Mariners on Sunday, followed by a home clash against Sydney FC three days later and the Reds' epic schedule culminates in Adelaide on January 2 with the top-of-the-table clash against Brisbane Roar.

Coolen's has backed Newcastle boss Branko Culina's calls for the FFA to review scheduling after the depleted Jets were thrashed 4-0 by Wellington.

Coolen said A-League clubs didn't have big enough squads to sustain such a heavy schedule.

He also warned the effects of excess fixtures may not be felt until much later in the season.

"I am used to working with a bigger squad, like in Europe for example," Coolen said.

"Sometimes you have a midweek game but not two weeks in row. It's something to think about in the future.

"I don't know how we're going to change it but for the players there's already a lot of pressure on them for the whole season with a small squad.

"You can't change players, especially when you play a lot of games in one week. Sometimes you could give players a rest and get them ready for the next game but we can't so we have to manage it.

"I think what makes it heavy is that we have small squads. There's a lot of games in a small period with a lot of travelling so you need a couple of days to recover from that.

"It may not affect you directly in a game but also it could be there in a couple of months."

The Dutchman acknowledged it wasn't a problem reserved just for United with every A-League club enduring similar crammed scheduling.

Coolen admitted the task had been made a little tougher with defender Daniel Mullen ruled out for the rest of the season with a serious knee injury.

Robert Cornthwaite is expected to start after a hamstring strain last week and stopper Nigel Boogaard will also return to the squad for the first time since Week 2 after a serious ankle injury.

After United were stunned 2-1 by Melbourne Heart at home on Friday night, they now trail league leaders the Roar by 10 points with two games in hand and Coolen conceded the Reds would need to take as many points as possible during the Christmas period.

"It will be tough, so many games in only a few days. We're not the only team to do it but it's not so easy," he said.

"They are important games for us. A few are away games and there is a lot of travelling and the squad is not so big at the moment so we have to be careful but our schedule is planned for that.

"You have to get your points every game and sometimes a draw is a good result in an away game. The challenge is to get your three points and that's what we're going for as well.

"We have to work with a smaller squad but you have to manage it your sessions. We haven't had a lot of injuries this season."