Kottaras was designated for assignment by Milwaukee on Thursday when they chopse to keep Martin Maldanado as the backup to Jonathon Lucroy.
The 26 year old De Los Santos was optioned to Triple-A Nashville. To make room for him on the 40-man roster, the team shifted right-hander Shaun Marcum to the 60-day disabled list.
De Los Santos has a 4.21 ERA and 46 strikeouts in 36 1/3 Major League innings for the Oakland over the past two seasons.
He has a 7.25 ERA at Triple-A Sacramento this year.