Allowing female soldiers to fight on the front line would be a "foolish move" that would be "paid for in blood", an ex-army chief has said.
Former Colonel Richard Kemp said women would be a "weak link" and claimed many soldiers would quit if the "social engineering experiment" went ahead.
The government is currently reviewing the ban on women serving in close combat roles.
The Ministry of Defence declined to comment on Col Kemp's remarks.
Women can currently serve on the front line, but not where the primary aim is to "close with and kill the enemy" - ruling them out of serving in the infantry or armoured corps.
Defence Secretary Michael Fallon has said he hopes to "open up combat roles to women" in 2016, saying roles "should be determined by ability and not gender".
The government's review, due to report back this year, is looking at the training procedures and physical demands of fighting to ensure any change can be made without damaging female soldiers' health.
Writing in the Telegraph, Col Kemp, who led the British forces in Afghanistan in 2003, argued: "This foolish move will reduce the capability of the infantry, undermine our national defences and put lives in danger."
He claimed only "a very small number" of women wanted to join the infantry, and that only "a fraction" of those would have the physical capability to do so.
But the move was being pushed by "politicians desperate to be seen as 'progressive', feminist zealots and ideologues hell-bent on equality of opportunity without exception", he said.
Col Kemp said it would be "extremely dangerous" to change fitness tests - as has been reported - to take account of differences between men and women, saying physical fitness was paramount to infantry soldiers.
Fitness standards: full MoD list.
"Through no fault of their own, women will often become the weak link in an infantry team. The men will have to take up the slack and this will engender resentment and reduce the cohesion that is so vital for effective infantry combat," Col Kemp wrote.
He added: "Every infantryman knows that the price for this social engineering experiment will be paid in blood."
However, Chief of Staff General Sir Nick Carter has told the Sunday Times there would be "no lowering of training or qualifying levels for soldiers in ground close combat roles".
Col Kemp has previously argued that women lack the "killer instinct" necessary to fight in close combat.
Armed forces minister Penny Mordaunt - the first woman to hold the post - has insisted that women "can make the grade".