According to ESPN and Derek Fisher, he is close to returning to the NBA after finding a suitable situation with an NBA squad. Two thing indicate to me it might be with the us.
1. The team isn't named in the report. Obviously signing with the Celtics would hurt his Laker legacy, and the reason the story isn't title "Derek Fisher Reportedly Close to Returning to The NBA with the Boston Celtics" is so he won't tarnish his legacy unless he is certain the deal is solid.
2. The celtics have a roster spot open and need a back up point guard.