Speculation has claimed that Tottenham are trying to sign the Argentina international in a reported €30million (£25.8m) deal as a possible replacement for Gareth Bale.
However, Garcia is keen for the 23-year-old forward to remain at the Stadio Olimpico after seeing Daniel Osvaldo leave Roma for Premier League side Southampton.
"I won't change what I said pre-season, which is that I wanted all the players in the squad to remain, but this is not the day to talk about the transfer market," said Garcia at a press conference ahead of Sunday's Serie A opener away to Livorno.
"There are two aspects to be considered: sporting and financial. At times the financial aspect comes first. I always consider the transfer market to be the worst time for a coach and the fact our season begins before the session has closed is irritating.
"We are working along with the directors and I trust they will give me a competitive squad."
Regarding Lamela, Garcia added: "Every coach would love to have a player who scores 15 goals per season and who is a regular in the Argentine national team.
"Erik is in the squad, exactly like the other 22 players. I can't do anything about the transfer market, so I am concentrated on tomorrow's game to start with a win.
"I have faith in my club because this will be a strong Roma, which is important for the fans and for all of us. I trust the club will give me options, so if someone leaves he'll be replaced by someone of the same level."