The creator of Grand Theft Auto has warned there might be teething problems as its online version launches.
Last week Rockstar North admitted it was facing "unanticipated" pressure because sales of GTA 5 had been stronger than expected.
"We are working around the clock to buy and add more servers," its blog said.
But it added that matters could be "more temperamental than such things usually are" because using so many computers introduced their own issues.
In the online version of the 18-rated violent crime game, up to 16 players can interact simultaneously within a virtual environment and create personalised avatars.
It is included free with every copy of the GTA 5 console video game. According to one analyst's figures, more than 15 million units of the title had been sold by early last week.
"At a conservative estimate I would expect about two million players to log on to GTA Online within the first 24 hours," added Keza MacDonald, UK games editor for IGN.com, the video game and entertainment site.
"Rockstar has never done an online game of this scale before, so they are totally unproven in terms of their network infrastructure.
"And even the highly successful World of Warcraft at its peak didn't have as many people playing online at once as GTA is likely to have, so it wouldn't surprise me if there were problems."
Other bestsellers have faced issues after their servers failed to cope with demand.
