The Colombia striker missed the 3-1 home defeat to Manchester United last weekend after suffering a groin injury during the Capital One Cup defeat at Leicester on October 29.
The 28-year-old was initially expected to be out for around a fortnight but he is now facing a longer absence after undergoing further tests.
Fulham have scored only 10 goals in 10 Premier League games this season and Rodallega's injury is a blow to Cottagers boss Martin Jol as his side look to revive their flagging fortunes.
Rodallega has yet to score in the league this term although he has netted three times in the Capital One Cup, including a double in the game against Leicester.
Centre-back Brede Hangeland has, however, returned to training and is in contention to start against Liverpool at Anfield on Saturday.
The Norwegian has not featured for Fulham since being forced off at half-time during the 4-1 victory at Crystal Palace on October 21.