The Blues boss has admitted the defender's challenge was against the laws of the game, but added that worse infringements are committed every week
The Brazilian clattered into the 19-year-old during the Blues' 4-0 fourth-round FA Cup victory over the League One side at Stamford Bridge.
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The Spaniard told reporters: "I see hundreds of tackles in the league that are more dangerous than that one. I won't say it wasn't bad – it wasn't the best – but a factor was the size of the other player.
"David Luiz is a great player and we have to be pleased he's playing in the Premier League. It was bad luck."
Reeves made his return for Brentford reserves against Bristol City on Tuesday after doctors cleared him from any serious injury.
Luiz went into the dressing room to apologise for the challenge after the match, but Reeves himself is still unhappy - suggesting the Brazil international's actions were deliberate.
He added: "If you watch it again it does look like Luiz meant it and went for it, even if he realised afterwards it was wrong.
"I remember passing the ball off and I got a shoulder straight in the face. My head was all over the place and I started wobbling around like a boxer who had just been knocked out.
"I must have only been on the pitch for about eight minutes and then had to go off, so I wasn't very happy."