In a related move, the Oilers have assigned Gaetan Haas to the Condors.
Gagner returned to the Oilers in a trade with the Vancouver Canucks for Ryan Spooner last February.
The 30-year-old — who was drafted by Edmonton sixth overall in the 2007 NHL Draft and spent the first seven seasons of his career with the club — recorded 13 points across 32 games with the Canucks and Oilers combined in 2018-19.
In four games for the Condors this season, Gagner has two goals and two assists.
Haas agreed to a one-year, entry-level contract with Edmonton in July.
The 27-year-old has appeared in 392 Swiss National League games with SC Bern and EHC Biel-Bienne, posting 192 points (72 goals, 120 assists) and 104 penalty minutes.
In five appearances with Edmonton this season, he has registered one assist.