Bosnich, 36, has a fortnight to convince the Mariners he deserves a chance as a guest player.
"It's the beginning of the beginning," Bosnich told reporters on Friday.
"I just have to give myself the best chance possible. We'll see what happens from there."
Bosnich said he had got a good feeling about being back in Australia 15 years after he last played for Sydney United.
"Sometimes you don't miss something until it's gone, or until it's taken away from you," said Bosnich, who played 22 times for the Socceroos.
"Playing at such a high level for such a long time, you can take things for granted. So it's nice to be back home to try and start again. It's an environment where I do feel safe, and around people who like me," he said.
"I think I'm ready to play, but I am on trial, and I think that's right given what has gone on in the last five years.
"But I'm the type of person who performs best under this kind of pressure. I'm looking forward to this. If they decide it's not to be, but hopefully it will work out OK."
Bosnich said he spent the past three weeks working out with a kick-boxing trainer in London, and said he needs to lose another two kilograms to play again.
"I think my fitness is quite good, what today showed me is that I need to improve on some hand-eye combinations, and getting my feeling for positional play, but that will come in time," he said.