In a separate move, right-handed pitcher Nick Kingham has been designated for assignment.
Buchholz had been dealing with a Grade 2 strain in his right shoulder since early May. The 35-year-old has a 6.57 ERA, 1.54 WHIP and 12:6 K:BB through 24.2 innings this season.
Giles was placed on the paternity list on August 22 and, after spending a few days away attending to the birth of his son, will make his return to the Blue Jays. On the season, he boasts a 1.80 ERA and 1.13 WHIP while striking out 65 across 40 innings.