The Turkos bounced straight back to the Primera Division after being relegated in 2011, and will make the young Portugal midfielder their first transfer of the summer
The Turkos confirmed in their official newspaper that the Portugal international, 23, would be spending the 2012-13 Liga season at Riazor after an deal was struck on Saturday afternoon.
Under the terms of the agreement, Santos will sign for 12 months with Deportivo, and the transfer will include an option to make the switch permanent at the end of the spell.
Santos has been with Sporting since the age of 11, and has impressed as a midfielder for the Lisbon institution. He made his international debut in 2011 with Portugal, and to date has appeared twice for the senior team.
If the signing is made official, it will be Deportivo's first purchase since confirming their return to the top flight following an absence of one year.
The club secured a comfortable promotion from the Segunda at the first time of asking, picking up 91 points from their 42 games.