In Zynga's first month or so of trading, its stock from an IPO price of $10 to a price of around $8.90 today.

This happened because Zynga's bookings (more important than revenues) and user growth have stalled.

It needs help.

It could be on the way.

The Justice Department recently opened a door that lets states allow some forms of online gambling.

We'd heard there was a lot of talk within Zynga about the opportunities of introducing online gambling into some of the company's games after the ruling. It already has the infrastructure in place to build a game and rapidly scale it out.

Now that the law is out of the way, Zynga could have an opening to build games that support some kind of online gambling. Imagine betting real money in a Zynga Poker game — and actually making money off playing a video game on Facebook.

Zynga already has a poker game — Texas Hold 'Em, which has 29 million players, according to AppData. Many other kinds of gambling games are naturally social.

But just how big is the opportunity exactly?

Well here are some examples of other online gambling companies:

PartyGaming was the dominant online gambling company in 2005. The company's poker business brought in around $860 million in revenue. That company was founded in 1997.

The same Forbes report suggested FullTilt Poker generated around $500 million in revenue annually.

One counterpoint: Betfair, an online betting exchange, only brings in $34 million from Poker and $510 million in revenue overall last year.

So let's call this a billion dollar revenue opportunity. That's a lot for Zynga, which didn't generate a billion dollars in revenues during the first 9 months of 2011. So…w ill Zynga seize it?

A source close to Zynga told us the company isn't ready to act on it yet — or CEO Mark Pincus would have already made a move internationally where the laws aren't as strict. Zynga also doesn't want to alienate its player base by introducing gambling between friends, a source close to the company who asked to remain anonymous told us. But a source close to Zynga with a lot of influence at one point in the company's history said it would represent a huge opportunity for the company.