Gregory said: 'He's acted like a prat once this season, which he is eternally humble about. But he realises what an error he made that day. He tried to ref that game. I spent 18 years trying to do the same, so I told him you can't win.
'I hope that's sunk in because he's a smashing kid who's a very good footballer. He's more mature these days. He really has come on and I know he's desperate to get back into the England squad.
'Lee showed at Bradford what he's good at. In that last 20 minutes or so, he is the last player you want against you.' Those final lung-stretching stages provided Hendrie with a chance to exploit a lush killing field when he picked out Julian Joachim's darting run for Villa's third goal.
'Yeah, I enjoyed myself and I'm enjoying my football,' said Hendrie. 'Injuries set me back last season but now I feel I'm a lot better and stronger. There's a confidence to my game again.
'I want to get back in for England, of course I do. It's a matter of biding my time. Merse has been magnificent. His experience has helped a lot and I'm still learning from him. I hope I'm that good when I'm his age.'
Gregory's gamble looked shaky in a first half that had Bradford boss Jim Jefferies purring over the kind of neat, effective passing style he has pinned his hopes on.
But Rob Molenaar's misplaced pass out of defence led to Darius Vassell's first Premiership goal five minutes into the second half and Gary Walsh's poor clearance to Vassell soon after was punished by a searing finish for the England Under 21 player's second.
A Dean Windass first-half header past the far post was the nearest they came to ending a sequence of five scoreless games.
Jefferies admitted: 'Villa's first knocked the stuffing out of us. Heads went down and we collapsed.'
