A police spokesman confirmed the arrest but declined to name the person or give their nationality.
On Monday, the global athletics body IAAF said that both Dibaba's coach, Jama Aden, and a Moroccan physiotherapist were in police custody on suspicion of administering illegal substances to athletes.
IAAF officials have also carried out doping tests on 27 international athletes training in the city of Sabadell, 20 km north of Barcelona, where the three were arrested, police said.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Dibaba, 25, the sister of triple Olympic distance champion Tirunesh Dibaba and Olympic silver medallist Ejegayehu Dibaba, is the favourite to win the 1,500 metre event at the Olympic Games in Brazil in August.
Russia's team has been suspended from the athletics events in Rio because of doping allegations in track and field.
World Anti-Doping Agency (WADA) chiefs said on Monday they would call for “serious” action against Russia before the Rio Games if a new investigation next month shows evidence of widespread state-sponsored doping.
(Reporting by Angus Berwick; Editing by Mark Heinrich)
