Brisbane Roar have added a back-up goalkeeper to their stocks, signing Vedran Janjetovic as an injury replacement.

The Roar will have a bit of inside knowledge on Sunday's opponents Sydney FC after signing the Sky Blues' former youth goalkeeper Janjetovic on a short-term deal today.

The 22-year-old gloveman comes in to replace Liam Reddy on a three-week injury-cover contract while the Roar's number one recovers from a thigh injury suffered against the Gold Coast two rounds ago.

Although too old to help Sydney retain their National Youth League title this season, Janjetovic has been training full-time with the first team and was excited to get the call from Brisbane last week.

"I jumped at the opportunity and came straight up," the Croatian-born shot-stopper said.

"I had a few training sessions with the guys last week and found everyone pretty friendly and easy to get along with so I've enjoyed it so far."

Janjetovic will provide some healthy competition for Griffin McMaster, who got his first start of the season in Reddy's absence against the Central Coast Mariners on Saturday.

McMaster will look to keep a tight grip on his place between the sticks against Sydney, but Janjetovic said he was ready to take whatever chance came his way.

"You have to sit back and wait for your chance," he said.

"Anywhere you go you need to show yourself to the coaches and everywhere you go you start from square one.

"So chances like this are good. You come in, prove yourself and if you get a shot you take it as best you can.

"If I do get any game time I'll approach it like any other game and concentrate on what I have to do."