Garcia, 20, came through Barca's academy before leaving for City in 2017 but has run down his contract and has not featured for Pep Guardiola's side in the Premier League since late November.
"I'm sure he'll come for next season and if it's not possible in January then we'll accept that and move on," Koeman told a news conference ahead of Sunday's La Liga game at home to Athletic Bilbao. Koeman said his Barca squad, who have won their last four league games and have also reached the Copa del Rey quarter-finals, need some reinforcements after players such as Luis Suarez and Ivan Rakitic left the club last year.
Barca beat Athletic Bilbao 3-2 in their last league meeting earlier this month but then lost to the Basques after extra-time in the Spanish Super Cup final.