Thailand's Buriram United, who travel to face Japanese side Vegalta Sendai in Group E, are still waiting for the result of a Thai Football Association (FAT) investigation into claims matchfixers tried to rig the result of their FA Cup final against Army United in November.
FAT head and FIFA executive committee member Worawi Makudi said last week that the Japanese official in charge of the final, which Buriram won 2-1, had reported to the Asian Football Confederation (AFC) that he had been offered money to help rig the result.
However, the AFC told Reuters on Monday that they had not received a report from Toshimitsu Yoshida so there was nothing for them to investigate.
Buriram chairman Newin Chidchob vehemently denied the accusations surrounding the victory that booked them a place in the ACL and criticised Worawi for hiring foreign officials.
"Both sides have spent huge sums to create their teams and we are not crazy enough to do such a thing," Newin told the Bangkok Post.
"Worawi should be the first person to take the blame because he hired foreign referees to officiate the match.
"They come and return home and do not have to shoulder responsibility. On the other hand, if Thai referees make an error, they could be punished."
Worawi had said he would report the issues to the AFC and FIFA at an INTERPOL conference into matchfixing in Kuala Lumpur last week.
The accusations of attempted matchfixing were another blow to Asian football which has been forced to deal with the problem recently in China, South Korea and Malaysia.
Also in Buriram's group, South Korean champions FC Seoul begin their campaign at home to Chinese Super League side Jiangsu Sainty.
Korean teams have won three of the last four ACL titles with Ulsan Hyundai easing through undefeated to take the crown in a home final against Saudi Arabia's Al Ahli in November, but a fifth placed finish in the K-League means they will not be back to defend their title.
Suwon Bluewings, who twice won the ACL's forerunner (Asian Club Championship), travel to face Australia's Central Coast Mariners on Wednesday with new coach Seo Jung-won optimistic North Korean forward can Jong Tae-se can lead them to glory.
"I will do my best to make sure we show the real Suwon, the Suwon who can conquer Asia," said Seo, who played for South Korea in two World Cups.
"Jong Tae-se is the kind of player who is ready to sacrifice for his fellow players. I am expecting that he will be a great help to our team," the coach added of his new signing.
Al Ahli do feature again and are expected to go deep into the competition, which has scrapped the heavily criticised one leg final format played at the home of one of the finalists.
The Saudis start their campaign at home to Qatari's Al Gharafa on Wednesday with former France striker Djibril Cisse expected to make his bow in the tournament for the visitors, whose manager Alain Perrin quit last week.
Having managed to hold on to most of his expensively-assembled squad, World Cup-winning coach Marcello Lippi will be hopeful of improving on Guangzhou Evergrande's quarter-final exit last season. The Chinese champions host J-League side Urawa Red Diamonds in Group F on Tuesday.
Al Ain have struggled in the tournament since winning the inaugural title in 2003 but the United Arab Emirates side look well placed to challenge once again.
With Ghanaian Asamoah Gyan leading the attack and talented midfielder Omar Abdulrahman turning heads, the UAE champions should cause Saudis Al Hilal problems in Group D on Tuesday.
The final, over two legs, will take place in October and November with the winner advancing to the FIFA Club World Cup.
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