The withdrawal from Germany was meant to be a cost-cutting measure which would offset the impact of closing two Scottish air bases
However, senior Ministry of Defence sources have admitted there could be delays in bringing the troops back to the UK.
Concerns over the plans have already been raised by members of the Defence Select Committee.
An MoD source said the target of getting half the 18,000 troops stationed in Germany back by 2015 is going to be "tight" and "challenging," particularly after the protracted behind-the-scenes rows over the review of bases and where troops should be stationed.
The army is also yet to give the Germans the two-year notice required to leave bases such as Fallingbostel where the Scottish battalions the Highlanders and the Royal Scots Dragoons are based.
It is understood Scotland will be the home of one of the new mobile brigades, probably doubling the number of army personnel north of the Border to around 6,000 at a time when around 2,500 RAF personnel are being made redundant or moved out.
The source said the move to Scotland will require the building of new accommodation at former RAF Kinloss in Moray, which has been closed because of the cancellation of Nimrod, and either RAF Leuchars in Fife or RAF Lossiemouth in Moray.
"There are a number of things that will need to be done in terms of new buildings, including at RAF bases, as well as infrastructure and sorting out school places as well as the process of leaving Germany," the source said.
"That means there will be no actual savings for about ten years, but after that there will massive savings coming in."
The source added: "The last government was looking at this as well, they just planned to do it more slowly which would have meant it would have taken longer to make the savings but cost less in the short term."
It is also understood that the move will be a "two-stage process" with the troops initially withdrawn to existing bases, but in the longer term taken to a "super garrison" town, such as Catterick, North Yorkshire.
A super garrison is the army's preferred option for a brigade in Scotland, which could jeopardise the long-term future of bases such as Leuchars, Kinloss or Lossiemouth, as well as RM Condor in Arbroath, which is expected to be transferred from the Royal Marines to the army in the next few years.
Clive Fairweather, a former SAS commander who is stepping down as an honorary colonel of the Argyll and Sutherland Highlanders, said: "A lot of this is political because the government wants to be able to tell the SNP to shut up by putting a lot of squaddies into Scotland and increasing the military footprint.
"But it is hard to see where they could be moved quickly. The RAF bases will need to be reconfigured and have new buildings because the social structure of the RAF and army are totally different and have different requirements in terms of messes and accommodation and so forth.
"I know that the intention is to have them here as soon as possible but whether that can be achieved is another question, although I expect most of the brigade to be in place within two years, again for political reasons."
He added: "There is certainly going to be a lot of building work and when you consider that the MoD has been forced to make cuts you have to wonder where the money for it will come from."
SNP defence spokesman Angus Robertson, who has two of the RAF bases in his Moray constituency, said: "What I suspect we may get is an announcement with a paper number of army personnel based in Scotland but a delay in them actually coming back from Germany."
The SNP have also made it clear that if there is still a gap by 2015 when a referendum on independence is expected the issue will feature highly in the campaign.
Labour Dunfermline and West Fife MP Thomas Docherty, a member of the defence select committee who has campaigned for Leuchars, said the admission that there would be no savings for at least a decade underlined the problems.
"This was meant to be a cost-cutting measure," he said. "But the question will be whether there are any savings at all and when they come."