Local reports say the pop star, 22, was treated for an unknown condition after being taken from Zurich's Hallenstadion venue to a private clinic around midnight and released at 3 a.m.
She played to a sold-out crowd in Lyon, France, on Tuesday night and is scheduled to play at Marseille on Wednesday, E! Online reports.
Alenka Ambroz, a spokesperson for the Hirslanden hospital, confirmed to MTV, "Rihanna came yesterday evening to the emergency room" but "we do not know the details."
Rihanna is scheduled to open the 25-stop North American leg of her tour with Ke$ha in Seattle on July.