Security has been boosted to avert any potential trouble at tonight's top-of-the-table clash between reigning champions Instant-Dict and arch-rivals South China. Hong Kong Football Association (HKFA) officials said a Grade Z police presence - one inspector, two sergeants and 15 police constables - will be on hand for tonight's double-header at the Mongkok Stadium which begins at 6.15 pm with a match between struggling Eastern and Uhlsport-Rangers. 'We expect a full house or near full house and we have booked a Grade Z police presence. We are expecting 6,000 to 8,500 spectators at the Mongkok Stadium. This will be a big day, especially for the South China and Instant-Dict game,' said HKFA assistant general secretary Yung Hung-yau. The last time South China and Instant-Dict played at the Mongkok Stadium in the Senior Challenge Shield second round match in November, 8,500 spectators crammed into the stadium, and full house signs are expected to be put up before tonight's 8 pm kick-off. The HKFA is concerned with possible crowd trouble, especially in the wake of the recent league match between Instant-Dict and Sing Tao at Mongkok which saw disgruntled fans throw missiles at the families of Sing Tao's expatriate players. It will be the sixth confrontation between South China and Instant-Dict this season. South China currently hold the edge with three victories. Instant-Dict have beaten the Caroliners once - a 2-0 win in the preliminary rounds of the Senior Challenge Shield last November. The last two encounters have ended in draws. South China striker Au Wai-lun is doubtful for tonight's clash after injuring his left leg during training yesterday. Brazilian central defender Aurelio is still recovering from a knee injury but will play tonight. Left-back Chan Wai-chiu will miss the game because of a one-match suspension. Instant-Dict will almost be at full strength, although there are doubts with Bulgarian forward Stefan Draganov, who was injured during his team's 4-1 win over Uhlsport-Rangers last week. Meanwhile, discarded Instant-Dict forward Dominic Iorfa is hoping to be signed up by Chinese professional side Guangzhou Apollo.