England and Harlequins full-back Mike Brown is still struggling to recover from the concussion he suffered against Italy in February.

Harlequins have brought in a group of specialists in an attempt to solve the worryingly persistent after-effects of Brown's collision with Andrea Masi in the Six Nations game almost 12 weeks ago. He has already been ruled out for the rest of the season.

Brown, 29, recovered sufficiently to face Scotland and France later in the series, but has suffered a recurrence of the symptoms since returning to Harlequins.

"We have had people in - a group of specialists who are experts in head injury - to look and see what the best way forward is for him," said Harlequins' director of rugby, Conor O'Shea.

"It will clear. You have seen instances already this year where it just takes time. With Mike's injury, as long as he's symptomatic, he's not fit, and he's still symptomatic."

As concerns about Brown's health continue to grow, calls for Nick Abendanon, the newly crowned European Player of the Year, to be recalled by England have become even louder.

Abendanon won the last of his two caps in 2007 and is theoretically out of contention due to an RFU ruling which states that English players plying their trade overseas cannot be picked for the national side, and Mike Ford, his former head coach at Bath, believes England manager Stuart Lancaster should stand firm while Abendanon continues to play for Clermont Auvergne.

Asked if the RFU should invoke the "exceptional circumstances" clause in their selection policy to include Abendanon, Ford said: "We've known for four years that there will be a World Cup in England, so I don't think these are exceptional circumstances. I understand why the rule is in place and it's a good deterrent. I think it's a good rule to have."