The warning came as the 20th Armoured Brigade prepares to deploy to the war-torn country this summer.
They are due to leave by the end of the year but experts fear they may have to battle their way out if the Taliban launch an offensive.
During pre-deployment training, soldiers have been warned that in a worst-case scenario the brigade could pull out of Camp Bastion under fire.
Senior sources said contingency plans have taken into account several scenarios including a withdrawal in contact – military-speak for a departure during a battle.
The 20th Armoured Brigade, dubbed the Iron Fist, made history as the last British unit to leave Iraq. It has now been selected to repeat the honour in Afghanistan.
Commanded by Brigadier James Swift, the 4,500-strong unit is based in Germany and is taking part in operational training ready for its June deployment.
It was one of the first units into southern Iraq on Operation Telic and under the command of Brigadier Tom Beckett was the last to leave in March 2009.
The force includes armoured, infantry and reconnaissance troops who are expected to be based in Camp Bastion and tasked with protecting the base while the remaining equipment is shipped back to the UK.
More than £25million-worth of gear from Camp Bastion is up for sale and advertised on an MoD website. Items on offer range from generators to tents and kitchen units.
To save the taxpayer money, defence chiefs also want to sell off hundreds of vehicles rather than to bringing them back to the UK
If it is not sold off some equipment will be handed over to the Afghans and other items blown up by bomb disposal specialists to stop it falling into Taliban hands.
Negotiations involving senior Afghan government officials and diplomats have been taking place to ensure that UK forces leave the country without being attacked.
And General John Lorimer, the head of British troops based in Kabul, is making sure the withdrawal of soldiers this year does not end in a battle as it did when British troops withdrew from Afghanistan in 1842.
Then the British garrison agreed a peaceful withdrawal of forces from Kabul but were attacked as they left. Thousands were killed and only one Brit survived.
A senior source said: “Planning is at an advanced stage but is constantly changing as we identify new constraints. It is a fact that we could have to fight our way out. It is something we need to be ready for but we want to avoid that.
“We will maintain overwhelming firepower with Apache and fixed-wing jets, which the Taliban cannot match. The aim is that the Afghan army will cover our backs.
“We expect the Taliban to make a lot of propaganda noise in the next few months as they try and win the information war but we don’t think they can generate a fighting capability that causes us concern.”