Well, why? A loan move doesn't make much sense at this point, without concrete assurances that he'll get playing time in a team, league, and system conducive to his abilities and honing them for the World Cup. For all the furor and hyperbole generated in the press about the January window, most teams are looking for short-term solutions to problems that have arisen since the summer shopping spree or issues that existed at that time and haven't been addressed.
A few major moves arise, but only if the right team comes in with the right transfer offer should Donovan even consider going overseas at this point. A loan could be just the wrong thing to do, if he went to a team in trouble looking for a quick fix and mired in volatility or a club needing a backup. Stewing on the bench or being hounded by fans desperate for a savior isn't the ideal preparation for a World Cup. He won't improve to any great extent unless he's playing for a top team in a strong league, and his chances of jumping into the starting lineup in those circumstances are slim, even though he's probably the only American field player capable of such a feat. Anything less, and he's better off staying put for the next six months.
If he stays in LA, he'll train with the national team in January, then report to the Galaxy, play regularly for a coach and a team and a league he knows well, and head off to South Africa in late May, after which he can sift through offers when the market is roiling in its quadrennial post-World Cup frenzy. At age 28 (as of next March), at the peak of his powers and with years of top performances pending, if his previous stumbles in Europe don't count against him, he'll find the right fit.
This past season, Donovan played his most consistent soccer in MLS, and shook off much of the complacency on which he'd glided for parts of his career. With just two months of league play between the start of the 2010 season and reporting for World Cup duty, he'll make every effort to be as fit and sharp as possible, driven perhaps by missing a penalty kick and losing an MLS Cup for the first time after winning his first MVP award.
Now, MLS has to do something about him sooner, since he's been "grandfathered" the past few years to earn a Designated Player salary even though he doesn't officially carry that designation. However, there's a sneaky way around that; with David Beckham on loan to AC Milan until after the World Cup and not available to the Galaxy, all MLS has to do is deem him "non-eligible," or something similar, and re-classify Donovan as the Galaxy's only "active" DP.
Come July, and the return of Beckham to the Galaxy, if a transfer is imminent, MLS can forego any official procedure regarding Donovan and bid him farewell when the time comes. That's assuming it hasn't already extended his exemption into 2010 and 2011, which are the option years on his MLS contract.
In a perfect world, he'd go to the right team in January, play a lot and play well, kick some butt at the World Cup, and settle into a lucrative and productive stint with a foreign club. But unless that seems more likely than not, he's best off right where he is.