SYDNEY Swans coach John Longmire has responded to criticisms of his use of the substitution rule, saying an underdone Shane Mumford was a key factor in the decision to use Mark Seaby as the designated sub against Melbourne.

The Swans were the only team in round one to employ a ruckman as their substitute, and Longmire said the decision to use Seaby in the role was made because of concerns over Mumford's knee.

"’Mummy’s’ knee was a bit sore last week. So you go into a game thinking it might be unfair to Jesse White … if something happened to ‘Mummy’, Jesse would be one-out on (Melbourne ruckman) Mark Jamar," Longmire said.

"Those things are all taken into consideration. At the end of the day you make a decision based on not only your substitute but also your other 21 players. We thought we had the flexibility to cover any scenario that happened."

The Swans coach said he doesn’t believe the new interchange rule, which allows for three interchange players and a sub, played a part in the Swans surrendering a 24-point lead to end up drawing with the Demons.

"We had a lot of the ball in that third term, and to only get three goals from 20 inside 50s to Melbourne’s 10, you know that is going to hurt you. You need to make the most of your opportunities when you get them," Longmire said.

The Demons used their substitute to great effect, with forward Ricky Petterd having an immediate impact. However, Longmire downplayed talk of Petterd's fresh legs as an advantage.

"Ricky Petterd was on the end of three centre clearances in a row, and twice he was on a young player in Gary Rohan so in the end it was not about running, it was more about body positioning," he said.

"I don’t think (the sub and interchange) played a big part in the result. But it would have played a big part if we had lost Shane Mumford and didn’t have a ruckman to go against Jamar.’"

In Swans’ selection news, defender Lewis Roberts-Thomson will play another reserves game before being considered for the senior side, while Tadhg Kennelly was also likely to play in the reserves practice game against GWS on Sunday.