Castleford are waiting to discover the extent of the knee injury sustained by leading try scorer Nick Youngquest.
The Australian winger, 27, took his tally to eight tries in seven games with a brace for the Super League leaders in the 52-20 win over Salford.
But the winter signing from Crusaders has picked up a knee problem and must now undergo scans this week.
"We're crossing our fingers because Nick has been a wonderful buy for us," said Castleford coach Terry Matterson.
Only Hull KR centre Kris Welham, on nine, has scored more Super League tries this season than Youngquest.
But having already missed one game with a quad injury, Youngquest will now miss Friday's meeting with Harlequins - and Cas hope he will not be out any longer.
"He definitely won't be playing this week," said Matterson. "He could be a bit of a concern."
The Tigers, top of the table after winning seven of their opening eight matches, have already had to cope this season without Australian utility man Ryan McGoldrick, who has been out with a knee injury.
Having made his comeback for the club's under-20s last weekend, he is now set to return to Super League action over Easter.
And Cas will also be without another of their close season signings, Willie Isa, for the trip to The Stoop.
The 22-year-old centre missed the win over Salford because of a one-match ban and his return will now be delayed for another fortnight after he ruptured ankle ligaments in training.
"We will be tested a little bit," said Matterson.
It says much for the current array of talent that the Tigers have not missed McGoldrick.
Despite operating on a shoestring budget, Matterson, who guided Cas to the play-offs in 2009, has taken the team to a new level this year despite the departures of high-profile home-grown duo Joe Westerman and Michael Shenton.
Matterson plugged the gaps with the signing of former captain Danny Orr, as well proven operators like Youngquest, Martin Aspinwall, Nick Fozzard and Warrington full-back Richie Mathers.
And the emergence of exciting youngsters Joe Arundel and Daryl Clark have provided an unexpected bonus.
"It's not one or two things, it's a whole lot of things," said Matterson. "We have had a bit of luck and we had a great off season.
"The newcomers all have a good work ethic, the young guys have come through quicker than we expected and those already there, guys like Kirk Dixon and Craig Huby, are all playing well."
Matterson, who took over at Wheldon Road following Castleford's promotion from the old National League in 2005, also believes that the club have got most things right off the field.
Despite being top of the league, Cas are, ironically, one of the clubs at risk when the Rugby Football League hand out the new three-year Super League licences in July.
One current club will be relegated to the Championship to make way for Widnes, who have already been given the nod to return to the top flight, and a second could follow if the RFL's board of directors decide that Halifax have a strong enough case for promotion.
The Tigers' new stadium will not be ready until the start of the 2013 season.
But, under Matterson, they are making an extremely strong case for a new licence on the pitch with their best-ever start to a Super League campaign.
"It's been tough," he said. "But we're a real good example of how the franchise system works. I think we're a blueprint for it.
"We're still not spending anywhere near the salary cap - our resources are stretched - but we're doing the best around what we have."