The biggest threat to the U.S. economic recovery may not be within its borders. Mortgage Bankers Association Chief Economist Jay Brinkmann said the stronger European countries such as Germany were unlikely to provide any more assistance for Greece, which would force it to default on its sovereign debt. "Greece will default. It's just a matter of when," Brinkmann said at the trade group's annual convention in Chicago Tuesday. "It would be kind of like asking the Tea Party to bail out the California budget deficit. It's just not going to happen." The consequence is a recession not only in Europe but possibly in the U.S. as well. Signs of one are already touching the euro zone because the austerity measures these troubled countries are taking, including Italy, Spain and Portugal. These sovereigns, right now, are living off of their ability to borrow money from other countries, and as that begins to dry up no new lenders will step in to continue growing debt levels, Brinkmann said. "It translates to other European countries because that was the money they were going to use to buy BMWs and other things built in Germany, so you're going to see a slowdown in Germany," he added. There is also the counter-party risk. As U.S. banks pull out of their exposures, European banks have begun to experience liquidity issues. Brinkmann said some of the most dire predictions is how much exposure U.S. banks must still unravel before the defaults begin. "How successful that strategy is to contain this will be very important for the U.S. economy. We will definitely see a slowdown in exports, a strengthening of the U.S. dollar. It may be enough to shove us back into recession. It's difficult to tell, but we're already operating very close to zero line," Brinkmann said. The issue facing German Chancellor Angela Merkel would be protecting the banks. Under current Basel rules, there are no capital requirements for sovereign debt, and the exposure to these problems was not included in the most recent stress tests. "I do think they will be able to set up some sort of ring around the banking system more so than Greece," Brinkmann said. Write to Jon Prior. Follow him on Twitter @JonAPrior.