Adelaide's first-choice keeper, Eugene Galekovic, will miss the match because of suspension, leaving 17-year-old Mark Birighitti as the only recognised keeper in the squad.
The Australians are confident they can score at home after netting three in last month's semi-final win over Uzkebistan champions Bunyodkur but know they have to keep a clean sheet to have any real chance of an upset.
"We've just got to do the best with the numbers we have," Adelaide coach Aurelio Vidmar told reporters on Tuesday.
"We know it's a very difficult task but you've still got to believe anything's possible."
Adelaide, the first Australian club to reach the Asian Champions League final, have been badly hit by injuries and suspensions in the lead up to the match, with only 15 fit players available.
Defender Angelo Constanzo is also suspended although midfielder Paul Reid is expected to be back after missing last week's match with an injury.
Vidmar said there was nothing the team could do about the players who were unavailable but he had urged his side to be more aggressive than in the opening leg.
"That's life. Frank Sinatra sang that didn't he? And that's how it is," Vidmar said.
"The players that are going in there are going to give everything they possibly can to try to reverse the result." Gamba Osaka's players arrived in Adelaide late on Monday and held a light training run on Tuesday.
Coach Akira Nishino said his players had been instructed not to sit back on their lead and push for an early goal.
"Three goals is a good advantage and to use this advantage to get the first goal is very important," he said.
