The 30-year-old, who scored 31 goals in all competitions last season, has not played for the Eagles since damaging ligaments in May.
"December is the aim but there are a lot of ifs and buts," he told the South London Press. "You never know because I haven't done any strenuous exercise for four-and-a-half months - that will be almost six by December.
"It has been pretty bad sitting and watching Palace in the Premier League but it is something I came to terms with pretty quickly over the summer period.
"I knew I was going to be out for a long, long time. Obviously it would be nice to be out there helping the boys - but it is nice to see them out there in the Premier League."
Palace are currently in 19th place in the table after six defeats in their opening seven matches.