England full-back Mike Brown says he is ready to move up through the gears in his World Cup preparation after showing no signs of headaches or pain during the recent training camp.
The Harlequins No 15 was knocked unconscious against Italy in the Six Nations in February but, having returned for the final two games against Scotland and France, was unable to play for his club again all season.
Concern grew as he struggled to recover from repeated headaches that caused moderate pain yet refused to lift, and he was told by Quins medical staff to rest at home, until it became evident his domestic campaign was over.
Brown is restored to full health after coming through two intensive weeks toiling at Pennyhill Park during phase one of the squad's World Cup training camp without symptoms of concussion resurfacing.
And he told Sky Sports News HQ: "The headaches seem to have gone now. If it was ever going to make a comeback it'd be in the training we're doing. Like 'Wig' (England forwards coach Graham Rowntree) said it's been brutal, it's been tough."
Brown will travel to Denver with the World Cup training squad that is set to depart for their two-week camp at altitude on Saturday - the party cut from 50 players to 45 the day before.
Mike Brown: To step up to contact in England training
Colorado will offer the first opportunity for the 29-year-old to experience contact since the rollercoaster Six Nations victory over France as England plan to play inter-squad matches.
He added: "I've been all-clear through that so hopefully the next stage will be to take a bit of contact, which I've got no doubts in my mind I'll be able to do.
"I can only speak for myself but if you believe you can put the effort in, get to the level then you'll get picked so that's what I'll concentrate on doing."
"Everyone's working hard to gel as a team but only 31 can make the final cut"
Alex Corbisiero
Northampton prop Alex Corbisiero also warned that the US-bound party are already playing for their World Cup places, ahead of the hosts' opening game of the tournament against Fiji on September 18 at Twickenham.
Corbisiero said: "That's the reality of the situation we're facing. It's so full-on, it's so competitive. There's so much at stake, everyone wants to be a part of it.
"Everyone's working hard to gel as a team but only 31 can make the final cut. The possibility of being involved is so great you've got to give everything."
Watch England v France, France v England, England v Ireland warm-ups from Saturday, August 22 on Sky Sports 1
