Fulham may be without midfielder Simon Elliott for the start of the Premiership season on 20 August.
Elliott made 12 starts for Fulham in the second half of last season
The New Zealand international, 32, hurt a calf muscle in the friendly win over Maccabi Petah Tikva in Austria.
Cottagers manager Chris Coleman told the club website: "Unfortunately, the only down side of the trip was that we lost Simon through a calf injury.
"We're taking every precaution with him to protect that and make sure we can get him back as quickly as possible."
Elliott impressed last season after arriving from United States side Columbus Crew in a free deal during the January transfer window and played in the first match of the tour before sitting out the draw against Real Madrid.
Coleman added: "It is disappointing but it is just one of those things that happen. Other than that we have been okay and the fitness levels of the players keep on improving every day."
Fulham face Germany's Borussia Monchengladbach and Portugal's Boavista on successive weekends before starting their campaign at Manchester United on Sunday 20 August.