Campaign group Women in Football says it is "appalled" by the Football Association's decision to take no action against Jose Mourinho.
The Chelsea manager was cleared of making discriminatory comments towards then club doctor Eva Carneiro.
The pair had a fiery confrontation on the touchline towards the end of the Blues' opening game of the season against Swansea, with Mourinho afterwards criticising Carneiro for going on to the pitch to treat Eden Hazard. Carneiro has since parted company with the club.
There had been suggestions Mourinho had used abusive language towards Carneiro but the FA, after having an independent academic expert in Portuguese linguistics analyse footage of the incident, announced it ''is satisfied that the words used do not constitute discriminatory language under FA Rules''.
A statement said: ''Women in Football (WiF) are appalled by the conclusion of the FA investigation into Jose Mourinho's conduct during, and following, Chelsea's match against Swansea on August 8, 2015.
''Contrary to the FA's appointed expert's advice, which WiF has not seen, our own language expert made it abundantly clear that the abusive words used by Mr Mourinho on the touchline that day were specifically directed towards a woman, as indicated by the grammar of his sentence.
"Other Portuguese speakers we contacted in gathering evidence also emphasised this point. We therefore find it extraordinary that any expert or Portuguese speaker would report otherwise.
''WiF can only conclude that this latest investigation provides yet another damning example of the FA failing to tackle discrimination, specifically sexism, in the football industry. Once again we are concerned by what we can only perceive as serious flaws in the process of such investigations.''
The FA felt moved to defend its process after Women in Football questioned its verdict.
The FA added: ''The linguistic was native Portuguese and has taught at the highest level universities in both Portugal and the UK with many published works on both Portuguese lexicography and lexicology and Portuguese linguistics including modern day vernacular.''
Mourinho was upset with Carneiro and head physiotherapist Jon Fearn for entering the field of play to treat Hazard in the closing stages of the Blues' 2-2 Premier League draw against the Swans.
That meant the Blues were temporarily down to nine men - goalkeeper Thibaut Courtois ahead already been sent off - after Hazard left the field.
Carneiro and Fearn were criticised for being ''impulsive and naive'' by Mourinho.
The Portuguese's comments attracted plenty of scorn, but the 52-year-old was unrepentant and earned further condemnation when it was announced Carneiro would no longer attend club matches or training sessions.
Earlier this month it was announced Carneiro had parted company with the Blues and it is understood likely she will launch legal action, claiming constructive dismissal.