Casinos in the state will be closed from 18 November to 8 December after a recommendation from the Department of Health and Human Services.
In October, Detroit casinos operated at 15% capacity and earned $101.4m, with $7.6m in sportsbook earnings also reported for October.
Analyst for MichiganSharp Geoff Fisk said: "The sports betting boom across the US comes from the popularity of mobile wagering. We likely won't see any states where retail sportsbook revenue comes anywhere close to what mobile wagering can produce."
According to MichiganSharp, Michican could earn close to an additional $30m per month from mobile betting. And online gaming could bring $650m in annual revenue.
The projections additionally factor in current figures from New Jersey and Pennsylvania, where online gaming and betting generated record revenue this summer.
Fisk added: "The pandemic can't shut down online gaming platforms. Mobile gaming is vital to the survival of the retail casino industry."
Michigan was prepared to launch statewide online sports betting, although the project has now been pushed back to December or even 2021.