Southampton manager Claude Puel lamented the double punishment of Nathan Redmond conceding a penalty and being sent off in Wednesday night's 4-1 home defeat by Tottenham.
Spurs led 2-1 in the second half when referee Mike Dean judged Redmond had deliberately denied Dele Alli a goalscoring opportunity.
Redmond had stumbled into the back of Alli as he was about to shoot and while Harry Kane blazed the spot-kick over, Tottenham made their extra man count, scoring two late goals to win the Premier League game 4-1.
New rules introduced in April state a team need not be punished twice for accidental fouls, but deliberate fouls - which include holding, pulling or pushing - still incur a red card.
Redmond appeared to fall into the back of Alli but it was difficult to judge if it was deliberate.
"I think it's a little hard because he didn't want to make a fault, he just touched the player," Puel said.
"It is two players trying to win the ball. It is difficult to accept because of course, it changes the philosophy of the game.
"After, it was finished. Against a team with this quality, good possession and great players, it was difficult for us."
Substitute Heung-Min Son and Alli's second completed an emphatic win after headers from Alli and Kane had earlier cancelled out Virgil van Dijk's opener.
Tottenham move one point behind Arsenal in fourth, while Southampton stay eighth.