The 27-year-old striker has been an integral part of Martin Jol's plans so far this season but has suffered a recurrence of a strain that has blighted him already this campaign
The news will come as a bitter blow to the 56-year-old Dutch boss, having seen the Costa Rican international restricted to just nine league appearances through injury so far already this term.
However, after aggravating his hamstring once again, he faces a further four weeks confined to the treatment table, as the club seek to end their recent run of poor form.
|TWO GOOD FOR THE TOON?
|17/2||Fulham are 17/2 to beat Newcastle 2-0 with Paddy Power|
"It's a big disappointment because Bryan is a vital player for us," Jol told reporters.
Meanwhile, right-back Sascha Riether remains a doubt for the club's home game against Newcastle on Monday evening, after he picked up a "minor knee strain" during the club's 3-0 defeat at Craven Cottage to Tottenham.