Fabio is currently on-loan at QPR.
While his brother Rafael seems to have raced ahead of him with his form for the Reds this season, the boss believes the pair could show parity again in the future.
"Ability wise, there's very little between the two," assessed Sir Alex. "But Rafael's got more experience now because he's played more games for us.
"Fabio's had quite a long list of injuries during his time here but I think in a couple of years' time, once he matures, he'll be fine."