The Magpies have been without the 25-year-old since September after he sustained a thigh injury, and Pardew has admitted that it will be another three months at least before the former Ajax man is fit to take the field.
He told the club's official website: "January probably is the earliest for Siem, so the Christmas programme looks out, which is shame because there's a lot of games in that period.
"We've got fingers crossed that he comes back in January ready to go because the injury he's got is such that we have to be very careful with his rehab and make sure that we don't put him at risk."
The 53-year-old believes that the loss of the midfielder has been detrimental to the Magpies this season, as he was brought into the club to replace Yohan Cabaye, who was sold to Paris Saint-Germain in January.
"He was obviously a massive signing for us. He was captain of Ajax, fantastic pedigree, yet to do it in the Premier League of course, but we have good confidence that he could and he is the link player that I think we've missed since Cabaye went," he added.
"It was a blow, but we have to ride those blows out and we have to be good enough to cope with it, and that's really where we are now - we need to step up to the plate and build on the win that we got on Saturday."
Newcastle face Tottenham Hotspur in their Premier League clash on Sunday.