Arsene Wenger says Gilberto only has a 20 percent chance of facing Newcastle on Saturday after returning to Brazil to deal with 'family problems'.
The Arsenal vice-captain missed his country's friendly with Switzerland on Wednesday night because of the issue, with young Gunners compatriot Denilson taking his place for the 2-1 win.
Gilberto has been a key figure in aiding Arsenal's transition to their new 4-5-1 formation so far this season, but Wenger now expects his midfield lynchpin to be absent for the visit of The Magpies at the weekend.
The former Atletico Mineiro star has flown home to deal with unspecified family concerns and his French boss admits the odds are against Gilberto appearing at Emirates Stadium.
"I believe we have a family problem with Gilberto. He has had to go back to Brazil," Wenger told the club's official website.
"We hope he will be back in time [for Saturday], but we are not completely sure.
"He had to pull out of the Brazil squad this week and I would say there is an 80 percent [chance] he will miss the Newcastle game."
However Wenger has received some promising news regarding another Samba star, with summer signing Julio Baptista returning to fitness after a six-week absence due to a hamstring injury.
The Real Madrid loan star has made just four substitute appearances for The Gunners so far, but could be included against Newcastle along with Freddie Ljungberg and Jens Lehmann - who are both fit after missing international fixtures in midweek.
"Nobody has come back from the internationals with any trouble," Wenger added.
"We have Julio Baptista back in the squad and Freddie Ljungberg is available too.
"We have had him on the phone and he says he is perfectly all right. Jens Lehmann is available again."