The Scotsman signed for Albion from RB Leipzig this summer but his career at the Hawthorns has got off to a stuttering start thanks to a hamstring injury.
"We're looking forward to getting Oliver in with some minutes under his belt and bringing him that much closer to selection," said Garner.
"He's a hugely talented player who has shown his potential at Nottingham Forest and has experience of playing in Germany.
"He gives us something different which we will definitely need at stages throughout the season. He can prove he's a capable Premier League player."