Despite going ahead against Perth Glory, the Sky Blues couldn't hold on conceding twice in the last seven minutes to lose 2-1 at Allianz Stadium.
It's been a tough few weeks for Sydney, losing both Corey Gameiro and Ali Abbas to season-ending knee injuries, while they were also without marquee man Mark Janko and defender Sasa Ognenovski against Perth.
With Abbas and Gameiro on the long-term injury list, the Sky Blues are scouring the globe for a couple of injury-replacement deals as Arnold looks to add better balance to his side.
"We've contacted our network of overseas agents to see what's available," the Sky Blues boss said.
"We've only got three foreigners here at the moment and we do have an area of positions to be able to use another two foreigners.
"We're getting emails every day, we're looking at them and doing our due diligence to make sure they are the right foreigners.
"The squad could be better balanced but it's not at this moment. We have to move forward this month and in January we can get two injury replacements for the two we've lost. We just keep battling away."
Sydney certainly had to battle in the first half against Perth, on the back foot for much of the opening 45 minutes.
But as has been the case for most of the season they lifted after the break and took the lead through a controversial penalty after referee Alan Milliner adjudged Glory's Dino Djulbic to have handled in the box.
They then squandered a couple of other chances to double the lead, before the Glory hit back through Rostyn Griffiths and an Andy Keogh penalty late on.
"We need to be ruthless and need to punish teams," Arnold said.
"We had them by the throat at 1-0 and could have strangled them but we let them off. We've probably ridden our luck over the last few weeks where we got away with some results but tonight it turned the other way."
Arnold was reluctant to talk about the penalty awarded to Perth three minutes from time which won them the match, but was critical about the circumstances surrounding the free-kick which led to Glory's equalizer.
"It was about 10 metres inside the field of where the foul was given," Arnold said.
"…I have to say that's the best we've played over the last three games. We've had disruptions during the week and overall a lot of positives to come out of it but disappointing to lose in the last five minutes."
Arnold was hopeful Janko will be right to return for next week's trip to play Melbourne Victory but was unsure if Ognenovski will be back due to an ongoing hip problem.