Speaking after watching the Sky Blues thrash Perth Glory 6-0 at Allianz Stadium on Saturday night, Arnold admitted all four deserved their chance.

Brazilian striker Bobo, Polish midfielder Adrian Mierzejewski, Serbian playmaker and reigning Johnny Warren medallist Milos Ninkovic and Dutch defender Jordy Buijs have been instrumental to Sydney's success.

Under AFC rules only three foreigners can be registered in a Champions League squad.

"We've got another six games before the registration of the foreigners so every game (counts)," Arnold told Fox Sports.

"I expect to win six games between now and then - and their performances will make that decision but at the end of the day it's going to be the toughest decision I've ever had to make because they're four wonderful players and all of them deserve to be in the squad.

"But that's the way it is, I don't make the rules and I'm sure whichever one (misses out) they will support the team enormously."

Arnold described Saturday's win as the best and most complete attacking performance by "any A-League team" after they piled on five goals in the second half . 

Bobo scored a hat-trick for the second game in a row. Adrian Mierzejewski was again masterful, getting on the scoresheet after having one scrubbed out for offside.

Ninkovic - last season's standout player - continues to work his way back from injury and Buijs is integral to the league's stingiest defence.

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Arnold revealed he challenged his championship-winning players during the week to win the match 6-0 and they did just that. Captain Alex Brosque and Brandon O'Neill joining Bobo and Mierzejewski - with his seventh in eight games - on the scoresheet.

"And I expected that, especially to be more clinical and to finish off 2017 in a fantastic way," Arnold said.

"I think that's 91 points from a possible 110 points in 2017. It's been a fantastic year and now we move on to 2018."