Youtube stars KSI and Logan Paul will fight at Manchester Arena with millions expected to watch online across the world.
Rt Rev Alan Smith of St Albans said the decision to place advertising for gambling firm MansionBet was "deeply worrying".
Speaking to the Telegraph, he said: "Gambling addiction is a major social problem costing the country millions and the majority of at-risk gambler are young men aged 16-34, to whom this sort of event is likely to appeal."
The event has been billed as the biggest ever internet event.
The vloggers are charging viewers £7.50 to watch.
Between them they have 37 million followers.
Stay up to date with the latest news stories from a Christian perspective. Sign up to our daily newsletter and receive more stories like this straight to your inbox every morning.