What has Robles done wrong really? Yeah he's looked dodgy but he's not made a fatal mistake that I can think off.
He has looked dodgy, which means to me that you shouldn't play him in a situation where if he does finally have that fatal mistake, that we all know he has inside him, it costs the team in the biggest way
If he botches a league match, it's not the end of the world
If he bollocks an FA Cup or Europa match, there's no way back
If Martinez wants to back him, then fair enough, but he deserves any critiscm that results if he has a repeat of his performances against Swansea and Arsenal