More than half (54 percent) of Brits plan to watch the World Cup online while at work, says Eclipse.
Research by the business ISP revealed that nearly three in five (58 percent) had given no thought to the effect watching matches online will have on their company's network.
Eclipse said will the majority of office workers watching the games live on the web, networks will dramatically slow down, and in some cases, may even crash.
"UK workers clearly want to watch World Cup matches live on their PCs. However, we advise all businesses to be mindful about the impact this could have on their day-to-day business operations," said Clodagh Murphy, director of Eclipse
"Streamed content uses a lot of bandwidth and this could seriously impact the performance of their business internet connection. It could take much longer to download important files or use business-critical applications such as e-commerce sites, email or online backup."
Furthermore, Eclipse also said that 56 percent of office workers had no idea whether their company had guidelines regarding watching World Cup matches live during office hours.
Just over a third (37 percent) believed watching the tournament online would not affect their productivity.
Eclipse said networks were most likely to be affected on Wednesday June 23, as England Plays Slovenia at 3pm on this date.
"We expect huge interest in that match as it is England's only group game that happens during the working day," said Murphy.
"It will be interesting to see how it impacts networks and connectivity. We suggest that all organisations develop robust guidelines on office computer use to avoid network congestion and slow performance of key applications such as Microsoft Exchange and SharePoint and also online data backup processes."
See also: Sony to film World Cup in 3D