Dec 20 (Reuters) - Australian shares settled lower on Monday as energy stocks fell on concerns over oil demand outlook, while fund manager Magellan Financial Group slumped to its worst session on losing a major client. The S&P/ASX 200 index (.AXJO) slipped 0.16% to 7,292.2, closing lower for the fourth session in five. Equity markets across Asia and crude prices sank as surging Omicron COVID-19 cases prompted tighter restrictions in Europe, threatening to disrupt global economic activity once again. "Markets are very cautious ahead of the Christmas break, with concerns about the impact of the Omicron strain," analysts at National Australia Bank said in a note. "More discontinuity in supply chains from Omicron could add to inflation concerns." Energy stocks (.AXEJ) dropped 3.4% in their worst session in nearly a month and were the top losers on the benchmark index, as oil prices slumped by more than 2%. Oil investor Washington H Soul Pattinson (SOL.AX) was the top loser on the sub-index, falling 6.1%, while gas producer Santos (STO.AX) dropped 4.8%. Magellan Financial Group (MFG.AX) plunged 32.9% after disclosing it had lost its largest client St James"s Place (SJP.L), which accounted for around 12% of the company"s annual revenue. read more The financial index (.AXFJ) lost 0.8%, with three of the "Big Four" banks down between 0.1% and 1.4%. Miners (.AXMM) rose 0.1%, with Rio Tinto (RIO.AX) adding 0.2% after the iron ore behemoth appointed a new chairperson. read more Dominic Barton, Canada"s outgoing ambassador to China, will replace Rio"s previous chair Simon Thompson, who stepped down to take responsibility for the company"s destruction of ancient rock shelters in Australia. Among other losers, construction firm CIMIC Group Ltd (CIM.AX) shed 15.4% before trading was paused by the stock exchange. After reports that the company had not paid wages and benefits to more than 100 employees, CIMIC said the employees were under the care of another company and it was working to ensure that they were compensated. Shares closed 13.4% lower after trade resumed. New Zealand"s benchmark S&P/NZX 50 index (.NZ50) finished 0.38% higher at 12,766.45.