By my count the LA Galaxy roster is currently full, with the in-season additions of Mastroeni and Hoffman. This means there will have to be an, as yet unannounced, corresponding deal.
Update: my bad, Courtois makes 30. Miscounted.
It is known that Charlie Rugg, Bryan Gaul, and Kenney Walker are all training overseas at Hammarby.
A loan deal for one or more of them would clear up the necessary roster space. No corresponding move is necessary now, but it will be if the Galaxy want to bring in a third DP. What it wouldn't do is clear up an international spot. It's possible Courtois would take up the last one the Galaxy have available, as LA traded one of two empty (at the time) spots to Colorado for Mastroeni. He doesn't take up an international spot, as confirmed by LA Galaxy Insider:
Worth noting, just confirmed that Laurent Courtois does not take up an international roster spot.— Adam Serrano (@LAGalaxyInsider) July 19, 2013
Update: LA Galaxy have officially announced the signing. The 34 year old will be available for selection tomorrow. No word yet on the corresponding move.