PORT Adelaide defender Jasper Pittard has been all but ruled out of Sunday's Showdown with an injured ankle and will have scans on Thursday to determine the extent of the damage.

Pittard hurt his non-preferred right ankle at training on Tuesday and was on crutches at the memorial service for Phil Walsh on Wednesday.

The 24-year-old has averaged a career-high 20 possessions in 2015 as one of the Power's prime movers out of defence. 

Midfield manager Michael Voss said the club wasn't holding much hope that the rebounding defender would be available on Sunday afternoon to face the Crows. 

"He had a bit of an accident at training the other day, a bit of a mishap," Voss said on Thursday morning. 

"We're certainly planning without him.

"With any ankle injury you tend to try and get off it straight away, so [being on crutches] is just good practice.

"We'll know in the next little while exactly where that all sits." 

Voss said there were a number of candidates who could slot into the side to either take Pittard's place, or allow the club to switch players around to fill the void. 

Both Andrew Moore and Nathan Krakouer were dropped last week, while Aaron Young's SANFL form last weekend was impressive.