But Gibbons expects the 35-year-old right-hander will pitch valuable innings.
"I've heard nothing but great things," Gibbons said Tuesday. "I've seen him a couple times on TV and really liked what I saw when he was pitching key roles for the Cardinals."
The Blue Jays and Oh finalized a $2 million, one-year contract on Monday.
Oh was 1-6 with a 4.10 ERA and 20 saves in 24 chances last year for St. Louis. He was 6-3 with a 1.92 ERA and 19 in 23 save chances for the Cardinals in 2016.
"No big problem, really," Oh said through a translator. "Some things didn't work out last season. It was just one of those seasons that I had a bad year, so I'll make it up this year."
The South Korean's deal includes a $1.75 million salary this year and a $2.5 million team option for 2019 with a $250,000 buyout. The second year would become guaranteed if he appears in 70 games this season.
Oh could make $500,000 in performance bonuses based on pitching appearances: $125,000 each for 40, 50, 60 and 70. He also could make $1 million in bonuses for games finished: $125,000 apiece for 25, 30, 35 and 40 and $250,000 each for 45 and 50.
"They've been throwing his name around for a while, his and many other guys, and then things just kind of fell in place," Gibbons said. "I knew he had signed with Texas (recently) and that fell through, and then we signed him."
Oh said the Blue Jays' quick completion of the process has motivated him.