Lobbe floored Armstrong after attempting to contest a ball up with North ruckman Todd Goldstein in the second quarter of the Power's seven-point loss at Etihad Stadium.
But Lobbe has only been fined by the MRP for the incident - handed a $1200 sanction with $300 suspended to reduce to total penalty to $900.
It leaves the 24-year-old free to take on Brisbane at the Adelaide Oval on Saturday afternoon.
Port Adelaide will host the Lions at 1:40pm.
