Police said Phelps was unable to perform satisfactorily a series of standard field sobriety tests.
The 25-year-old Spaniard has scored two goals in four matches since joining United from Athletic Bilbao.
Nadal enjoyed an emphatic return to singles action as he powered past Richard Gasquet at the China Open.
Coming off a 28-10 loss to the Boks, the Wallabies were left without baggage on arrival in Buenos Airies.
The Boks believe their improved fitness levels will make them a more dangerous side.
Thembani “Terror” Gqeku says the club teaches the young boxers valuable life skills.