Casemiro's second red card of the year required Manchester United to accept a 0-0 draw. Erik ten Hag criticized "inconsistent" officials at struggling Southampton on Sunday.
At Old Trafford, Casemiro received a booking for his high challenge on Southampton's Carlos Alcaraz before he was sent off in the 34th minute.
Andre Marriner, a VAR official, advised Anthony Taylor to study the foul committed by the Brazil player on the field monitor before the referee upgraded it to a red card.
United had to work extremely hard to avoid a shocking loss at bottom-of-the-table Southampton after recovering from their 7-0 humiliation at the hands of Liverpool last weekend by defeating Real Betis in the Europa League on Thursday.
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Casemiro saw a red card against Crystal Palace in February, and United manager ten Hag was incensed with the decision to dismiss the player. He also expressed displeasure with penalty decisions that didn't favour his club.
Ten Hag stated, "Now, what I think the inconsistency (means) is that players no longer know what the policy is".
"I believe everything is clear. You saw the Leicester-Chelsea game yesterday, right? Well, VAR isn't coming into play there".
"Today, there will be two penalty situations followed by a coming on the line, but they will not".
"I believe that the first one in particular was a blatant and evident handball for me; what is the policy?"
Ten Hag stated that he had "some issues" about the refereeing since Casemiro, crucial to United's chances of finishing in the top four, will now serve a costly four-match suspension.
Ten Hag said, "There's another one who's inconsistent. We are the Premier League, and we're going strong here, and the referees are coming at the beginning of the season with that policy".
"In more than 500 games across all European levels, Casemiro never had a red card, but he has already received two".
"He plays tough but fair, and he also plays fair here. That is highly disputed because it is the same as Crystal Palace".
"When you freeze, it seems horrible, but everyone who is acting on top of football and knows something about it knows what is bad and what isn't bad, what is fair".
"Casemiro is a highly fair player, I can tell you that. It depicts more than 500 games in the major leagues without ever receiving a warning".
Ten Hag answered, "we shall see," when asked if United would appeal a ruling that left United playing the best part of an hour with ten men.
"This team once again demonstrated great enthusiasm, teamwork, good fighting spirit, and mutual support. After the draw, he said, "I think we played with 11 and ten at an excellent level".
