Leeds Rhinos captain Stevie Ward has been stood down "indefinitely" as the club look to find out more about the concussion he suffered in the opening week of the season.
Ward, 26, has not featured since going off in the defeat by Hull FC on 2 February.
"He's failed his return-to-play protocols for the past three weeks," boss Richard Agar told BBC Radio Leeds.
"For him to still be showing symptoms after three weeks is concerning."
He continued: "As soon as he's started exercise, the dizziness and blurred vision have come back, so we're sending him down to see a specialist in London to have some more cognitive tests.
"The person we're sending him to see had 10 cases in rugby union last year of concussions that lasted three months. We're not saying Stevie is going to be out for three months but it tells you when you are dealing with things like this it is not straightforward."
Ward appeared in the 2012 and 2017 Super League Grand Finals for Leeds, who are his only professional club, as well as the 2015 Challenge Cup final.
"We're leaving this in the hands of the medical experts because it is certainly not one we can take lightly," Agar added.