Tadic felt Young should have been sent off, but referee Craig Pawson failed to spot the incident: 'Yes, but normally you can not see that.
Young accepted the charge on Sunday, and his argument the three-game suspension was excessive was rejected by a regulatory commission.
Asked if Young should have have been sent off, Tadic said: "Yes".
Young's ban means he misses today's New Year's Day fixture with Everton and then the potential banana-skin FA Cup tie with Derby. I didn't really understand.
They would also exit the Carabao Cup at the hands of Championship side Bristol City with a strong side and are now on a three-game drawing streak with the likes of Leicester, Burnley and Southampton holding the Red Devils.
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Young, who joined United from Aston Villa in 2011, returned to the England squad in November after a four-year global absence.
Swansea defender Kyle Naughton has also been charged with violent conduct by the FA for allegedly stamping on Watford's Stefano Okaka during the Welsh side's 2-1 victory at Vicarage Road on Saturday.
Several United players felt as though they should have been awarded a penalty when the ball struck Maya Yoshida's hand in the first half but Pawson waved away all protests.
'No, no, no, nothing, ' said the Southampton player.
"I know my players so when I see people like Mata nearly in hysterics I know, no doubt and then at half-time I watch it". It was long time ago. "You have to change, which is what we try to do".