Lowry, who also missed Friday's win over the Miami Heat, is out with a right foot injury. He had previously been considered questionable for the Pacers game, suggesting the issue ultimately won't be long term.
Siakam is sidelined with left knee swelling. During the Raptors' win against the Heat, Toronto's young star was experiencing what had been described as a groin injury. It is unclear at this time if the injuries are connected.
In 13 games this season, Lowry is averaging 18.2 points and 7.1 assists.
Siakam, after struggling to start the year, has averaged 18.6 points, 8.1 rebounds and 4.7 assists in 14 games.
You can watch the game between the Raptors and Pacers from Indianapolis on Sportsnet ONE beginning at 1 p.m. ET/ 10 a.m. ET.