The Brazilian has missed the last two games for City and in his absence the they have conceded five goals.
The Citizens lost both matches - to Crystal Palace and Leicester City - and have dropped to third in the table. The 2-1 defeat against Leicester was City’s third defeat in four games and means they now trail leaders Liverpool by seven points.
The reigning league champions will be hoping to close the gap to Jurgen Klopp’s men when they face Southampton on Sunday, and speaking ahead of the game, Guardiola confirmed Fernandinho has returned to training.
“Everybody is fit but some players have some problems,” he said in his pre-match press conference.
“We will decide tomorrow but Ferna, Gabriel Jesus and Kompany have been in training.
“I’ve said many times how important he (Fernandinho) is – his position and qualities. Of course, he is so important, like Kevin (De Bruyne). We have to find a solution to win games.
“We tried (to recruit back-up) but the market was not there and it didn’t happen.”
Fernandinho has been struggling with a thigh injury, but his return to the side could be a welcomed boost for Guardiola.
“We will have his (Fernandinho’s) qualities again and he is an incredible player,” said Guardiola. "He is so important like Kevin is, so of course he is important we have to find another solution if he is not available.
A win for City on the south coast could help close the gap on their rivals at the top of the table, yet playing a day after Liverpool and Tottenham allows the pair to increase their lead over the Citizens.
City have a good recent record against Southampton and beat them 6-1 earlier in the season.