Sigmund, who ran laps around the Phoenix's training paddock today and has experienced general soreness, doesn't strike anyone as the type of guy who would like to rest and miss a game.
"I don't know if he's capable of 90 minutes," Merrick said.
Merrick would also be loathe to pull apart his successful centre back pairing of Sigmund and Andrew Durante which has been solid all season.
"There's a few options. Our defence have been playing particularly well."
Manny Muscat will also return from suspension this week, which will give Merrick another option in defence if he does choose to shuffle the deck against the first-placed Glory.
But the Scotsman may just be trying to create doubt in the minds of Perth who will fancy their chances of toppling the Phoenix at home.
Burns appeared to run freely during last Saturday's 2-0 win over Adelaide but Merrick said he was limited by a hip problem.
"It's not a bad injury," Merrick said. "But the risk is they'll break down and be out for four-to-six weeks with a tear or a joint injury."
New recruit Joel Griffiths said he was fit enough to start a game but the veteran was unsure about putting in a 90-minute shift, if required.
Meanwhile, midfielder Roly Bonevacia, who has no injury concerns, needs to decide whether to take up an offer to play for the Curacao national team.
The 23-year-old, a Dutch youth international, qualifies for Curacao through his parents.
The 160th-ranked Curacao, previously known as Netherlands Antilles before that country was dissolved in 2010, will meet Montserrat at the end of the month during the next Fifa window.
Committing to a national side is a big choice. It's unlikely he would ever force his way in to the Dutch senior side.
If he was to make the journey to play for Curacao, he would also miss two A-League fixtures.
