Gomez is set to undergo a medical ahead of signing a four-year contract at the Etihad.
The 21-year-old is viewed as a development player by City and though he could stay in Manchester this season, he is expected to be loaned out to a City Football Group affiliate.
The Premier League champions therefore remain in the market for left-back following their failed pursuit of Brighton's Marc Cucurella, who joined Chelsea in a £62.5m deal last week.
Joao Cancelo and Kyle Walker are the only senior, recognised full-backs in Pep Guardiola's squad after the departure of Oleksandar Zinchenko to Arsenal in a £30m deal last month.
Borussia Dortmund left-back Raphael Guerreiro is among those being considered. The 28-year-old has only one year remaining on his contract at Signal Iduna Park.
Gomez is a product of Barcelona's La Masia academy, and subsequently joined Dortmund in 2018, making three senior appearances.
The Spain Under-21 international was named Anderlecht's player of the year last season, finishing third in the Jupiler Pro League under the management of former City captain Vincent Kompany.
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