The French left-back was given his marching orders after a bad foul from behind on Saints right-back Kyle Walker-Peters
The Toffees’ unbeaten start to the Premier League season came to an end at St Mary’s, with Ancelotti’s side already two goals down when Digne saw red.
Match referee Kevin Friend showed him a straight red card after stamping on the back of Kyle Walker-Peters’ ankle, but Ancelotti was furious with the decision.
“The red card was a joke, it was not intentional, for sure it was not violent,” Ancelotti said on Sky Sports.
“Maybe it was a yellow. Maybe all this talk all week against [Jordan] Pickford, against Richarlison, affected the decision and if so it’s not right, it’s not fair. We will appeal, for sure.
“I told the players winter is coming and we will have to react.”
Everton have been in the headlines over the last week after the fallout from their 2-2 Merseyside derby draw with Liverpool.
Goalkeeper Jordan Pickford’s challenge on Virgil van Dijk has left the Liverpool defender possibly out for the rest of the season, while Ancelotti was criticised by some for drawing attention to a Van Dijk tackle on James Rodriguez after the game.
Some of the positive feeling surrounding Everton at the start of the season has seemed to dissipate over the last seven days, and Ancelotti admitted his side were far from their best.
“We didn’t play well, Southampton were better than us and they deserved to win. Sometimes you are not at your best, it came after a really good run for us, now we have to look forward with the same spirit and belief.
“We tried to get back into the game, we had some good control after half-time.”
Everton’s next fixture is a trip to the north east to face Steve Bruce’s Newcastle.
Everton are still top of the Premier League table with six games played, but Liverpool are now level on points at the top following their win over Sheffield United.