De Los Santos was optioned to Triple-A Lehigh Valley on Tuesday.
De Los Santos had been with the team for most of August, allowing one run in 6.1 innings while striking out 10 and walking two in his latest stint with the team. The strong showing was only enough to bring his season ERA and WHIP down to 5.24 and 1.61, respectively. The move clears space for Freddy Galvis to return from his quadriceps injury.