After attending the Maple Leafs' training camp ahead of the 2009–10 NHL season, Reimer was again sent down to the AHL. As part of the Marlies' pre-season, Reimer competed in the Gardiner Cup, held as part of Scotland's 2009 Homecoming celebrations. He stopped 33 shots in the final as the Marlies lost 3–1 to the Hamilton Bulldogs. Back in the AHL, he spent the majority of the 2009–10 season with the Marlies, playing in 26 games and recording 14 wins. He had a GAA of 2.25 and a save percentage of .925. Reimer was called up by the Leafs on an emergency basis on October 13, 2009, when starting goaltender Vesa Toskala was injured. Serving as Joey MacDonald's backup, he did not receive any playing time in his first NHL call-up and was sent back to the Marlies on October 25. Reimer missed significant time with an ankle injury during the 2009–10 season. It was not the same ankle he injured during his final season with the Red Deer Rebels.