Fernandinho's deal will expire on June 30, so he'll be leaving the club if they don't offer him a new one.
Per James Robson of the Evening Standard, Guardiola said:
"I think at the end of the season we are going to decide on the situation.
"The players who finished their contracts, the players with full contracts, what we have to do is what we believe is the best for the club and organisation for next season."
City brought in Rodrigo from Atletico Madrid last summer as a long-term defensive-midfield replacement for Fernandinho, 34.
On paper, the Spaniard looked to be the perfect recruit for City in this position thanks to his blend of impressive technical skill and robust physicality.
However, as The Athletic's Sam Lee observed, he has struggled somewhat in the early months of his City career:
Meanwhile, a long-term injury to Aymeric Laporte early in the season prompted Guardiola to use Fernandinho as a makeshift centre-back.
The Brazilian has adapted to the new position well, and he has been keeping natural centre-back Nicolas Otamendi out of the starting lineup.
Per BBC Sport's Mike Minay, Guardiola recently explained his decision to keep Fernandinho in defence, despite having two fit centre-backs:
However, Robson believes City are missing him in midfield:
Whichever position he plays, it's clear that despite his age he's still a valuable asset to City.
However, he'll be 35 in May, and his time at the top level will likely be coming to an end soon.
Much could depend on how well Rodrigo performs for the remainder of the season. If he settles in and rediscovers the form he showed with Atleti and City strengthen their defence next summer, they'll be able to let him move on.
Should Rodrigo continue to struggle, keeping Fernandinho for another year could help them continue their transition.