The Brazilian twins, 23, joined United in 2008 but only Rafael has managed to earn himself a regular place in the starting lineup, although his season under David Moyes has been disrupted by injuries.
Fabio was sent out on loan to QPR last season and has been linked with a move to Cardiff City in January, and while the defenders' agent has dismissed those rumors he has claimed that things will change at the end of the season.
"I do not know anything about these rumors," Cassiano Pereira told Calciomercato. "I think that is just media speculation.
"At the moment I can say that they will remain in Manchester until the end of the season, but in summer it is very likely that they can go."
Fabio received a straight red card just moments into his third appearance of the season, the Red Devils' FA Cup third round defeat to Swansea on Jan. 5. It was his first outing since being brought on in the final minute of the Capital One Cup clash against Norwich on Oct. 29.
Rafael, despite becoming an integral part of Sir Alex Ferguson's starting XI in recent seasons, has featured in just nine Premier League matches and three in the Champions League this season, and has been substituted in half of those games.