Nichols said that while Wanderers took the opposition line-up and style of play into account to a certain degree in preparation for a game, the team's main focus was on getting their own approach right and playing to their strengths.
Asked what he thought Wanderers were likely to expect from Garcia, Nichols replied: "He's been there, done that, but I don't know how fit he is, I don't know old he is or anything, so it won't change anything we do.
"But hopefully it will have the right impact for the league that I think they're trying to get. I don't know if it's the right player, I guess we'll have to wait and see."
It is the second trip to Australia in quick succession for Garcia, 37, who scored twice for the Liverpool Legends in their 4-0 win over the Socceroo Legends in Sydney recently.
Nichols had a little joke at Wanderers goalkeeping coach Zeljko Kalac's expense when he said: "We'll probably have to watch him put the ball past 'Spider' in that Legends game."
Then, on a more serious note, he added: "We do some homework on each team we play, but we mainly focus on ourselves and we're confident about going out there and playing the way we want to play and playing to our strengths.
"We work on keeping the ball and getting in behind teams and if we do that well we know we're going to be hard to beat.
"It's about being tight at the back but also playing our game with the ball and creating chances, as we've been doing."
But, Nichols stressed, Wanderers need to do better at capitalising on their chances than they did in last week's big derby game, which they lost 2-1 to Sydney FC.
"We were frustrated at the end of the game because we knew we created enough chances to win," he said. "You don't want to lose any game, but when you know you could have easily won the feeling is even worse.
"The fact we created plenty of opportunities, that was something for us to take away from the game as a positive, but we've definitely got to improve our finishing because it cost us in the end."
Wanderers, after charging to the top of the table via an unbeaten run over 10 games from rounds four to 13, have lost their last two games. They were beaten 3-2 away to Melbourne City and that game, like the derby, was one they could have easily won.
"It's obviously disappointing to lose two games in a row, especially a derby, but I think our performances were probably good enough to win both games," Nichols said.
"That's a positive, but we've got to turn those performances into points because it's getting tight at the top and we can't keep dropping points."
Wanderers entered this round in second place, but with the potential to drop as low as fifth if they lost to Mariners and other results went against them.
"We've sort of let everyone back into it now," Nichols said. "So it's very important for us to start winning again."