The striker was expected back for Wednesday's League Cup clash, but that now looks unlikely.
The 22-year old posted the following message on his account today:
Can't walk. Can't stand. Constant sickness. @wattbike thanks— Connor Wickham (@ConnorWickham10) September 21, 2015
The summer signing has made just three appearances since his move from Sunderland last month, but had shown promise in those few outings.
Wickham missed out on his side's 1-0 defeat to Tottenham Hotspur on Sunday, and Palace boss Alan Pardew lamented his absence in his post-match interview.
“Connor Wickham is still missing, which is a bit of a blow because he started well,” said the Palace boss, in quotes published by the LES.
“We miss a bit of presence and nous… We are getting him up to speed and I will look to include him on Wednesday [against Charlton in the Capital One Cup], maybe to get some game time in him.”
The striker’s latest tweet would suggest a feature on Wednesday is highly unlikely, in what will serve as a further blow to Pardew.
Palace had their moments against Spurs and would have had a goal if it were not for Hugo Lloris’ superb save from a Bakary Sako strike, but they failed to sustain a constant threat.
The Eagles' pace on the counter is their main threat, but without a central figure - of the ilk of Wickham - to tie things together, the threat doesn’t always translate into goals.