Otto injured his back in the last quarter of last week's match against Sebastopol and has been ruled out for the rest of the Ballarat Football League finals season.

Swans assistant coach Adam Sewell confirmed on Wednesday that Otto had been ruled out for the finals series, having faced a number of back issues in the past.

"It's a big loss for us, that's for sure," Sewell said.

"He will be certainly missed.

"He's a great character around the club and to have in your side, but the back is well and truly gone for Joe."

Ballarat faces a sudden death final against Sunbury on Sunday in a repeat of last year's elimination final.

However, this year the roles are reversed.

Ballarat will go in as favourite, although the Lions are a massive threat with a number of big names to come into the side, namely VFL pair Daniel Toman and Jack Sheahan.

Up to 12 players are set to make their finals debut for Sunbury, in what has been a massive year of transition for the traditional powerhouse.

"There's nothing to lose for these guys. Most of them are going to be experiencing it for the first time," Sunbury coach Rick Horwood said.

"We haven't done pre-planning. It was all about just making the finals and now we are there we can throw everything at Ballarat."

The match will be played at Eastern Oval on Sunday at 2.15pm.