Junior only made his first-team debut for Betis in February, and has since scored twice in 15 La Liga appearances for the Spanish outfit.
The 22-year-old is regarded as a left-back but has played in central defence and as a winger for Betis B.
According to El Desmarque, City have scouted Junior on a number of occasions this season, and Guardiola wants to bring the Dominican to the Premier League champions to boost his defence.
The report adds that the Citizens would also not be put off by the £54m release clause which was included in the five-year contract Junior signed at Betis just last month.
Junior has played the full 90 minutes in all three of his club's La Liga matches at the start of the 2018-19 campaign.