The International Tennis Federation is "greatly concerned" ahead of next weekend's Davis Cup final between Great Britain and Belgium in Ghent after the Belgian government raised its terror alert to the highest level on Saturday.
The threat of terrorist attack is considered to be "serious and imminent" in Brussels and high across the rest of the country, with the Belgian Prime Minister, Charles Michel, telling a news conference on Saturday that the security level had been raised "based on quite precise information about the risk of an attack like the one that happened in Paris".
The British Foreign Office has updated its travel advice for Belgium, counselling that visitors "should avoid places where there is a high concentration of people".
The army and armed police have been deployed across Brussels, with the Metro in the city expected to be closed until Sunday evening, while this weekend's football matches have been cancelled. Ghent is just 30 miles from Brussels.
Andy Murray, who failed to progress into the knock-out stages of the ATP year-end championships in London, is scheduled to travel to Belgium on Sunday, along with the rest of the British team ahead of Britain's first final since 1978 and Belgium's first since 1904.
David Haggerty, the president of the ITF, said on Saturday that they would continue with their preparations for the three-day tie at the Flanders Expo, which is scheduled to start on Friday afternoon.
"Over the last week, the ITF has been in constant contact with the relevant authorities, the Royal Belgian Tennis Federation, the Lawn Tennis Association and our risk assessment company and this dialogue continues today," Haggerty said.
"We are aware that Belgium has raised the terror alert level for Brussels. This greatly concerns us but, at the present time, we are still continuing with preparations for the final. What I said last weekend is true today - security of players, fans, media and working staff remains our highest priority."
The Foreign Office has advised: "Following the terrorist attacks in Paris on Nov. 13 and subsequent police raids in Belgium and France, the Belgian government has increased its national threat level to the top level, very serious, for the Brussels region, indicating that the threat of a terrorist attack is serious and imminent.
"People should avoid places where there is a high concentration of people, particularly in the Brussels region, including concerts, large events, stations and airports, public transport, busy shopping centres.
"Follow the advice of local authorities and subscribe to email alerts for updates to this travel advice; the whole Brussels metro network will be closed on 21 and 22 November, many events such as football matches will be cancelled."