The Football Association on Wednesday confirmed referee Lee Probert had seen the incident which left Latics striker Di Santo with a large cut on his shin and led to his 74th-minute substitution at White Hart Lane on Tuesday night.
Because Probert chose to take no action at the time, the FA will not punish Spurs left-back Assou-Ekotto retrospectively.
Wigan boss Roberto Martinez said on Tuesday night: "It was a red card. It was high. Big decisions against us seem to get forgotten too easily.
"I was shocked and surprised when Lee Probert didn't show the red card because he was in a great position.
"We were very fortunate because Franco escaped the tackle with a minor injury and I've seen broken legs from (tackles like) that."