Allardyce faces a fight to prove he is the man to take the Hammers forward, with the club sitting second-bottom of the Barclays Premier League and ousted from the FA Cup after a chronically inexperienced side were trounced at the City Ground on Sunday afternoon.
It was Allardyce's call to name three debutants in his starting XI and send two more on as substitutes but, with survival the club's primary goal and a Capital One Cup semi-final first leg against Manchester City on Wednesday, he felt there was little choice.
The Hammers have major injury problems and are without suspended skipper Kevin Nolan, and Allardyce's team selection reflected where a second cup run featured in his agenda.
Nevertheless, the result proved an acute embarrassment.
"My hands are tied behind my back every time I see what's available and the team is almost picking itself. It's a disaster at the moment, a total disaster and in certain areas we've not been able to cope," he said.
"My priorities meant I put too many youngsters in and they were not able to withstand Forest's pressure in the last half an hour.
"I picked the team so it is my responsibility. But you know what my priorities are: the priorities are the Premier League first and then Capital One Cup.
"It's leg one on Wednesday and we need to get back to the second leg with an opportunity to get to Wembley and then get some points at Cardiff."
Poor results in both fixtures could leave Allardyce hanging by a thread and, although he had pre-warned co-owners David Gold and David Sullivan of his team rotation, he knows things must pick up.
"There might be (repercussions), who knows? It's their decision, not mine," he said.
"I'm not saying it won't happen unless I start to get results. I have got to get results, I know that."
Triumphant Forest boss Billy Davies, who saw Jamie Paterson score a second-half hat-trick bookended by Djamal Abdoun's penalty and Andy Reid's late effort, was rightly proud of his charges.
Bookmakers made the home side favourites after the team-sheets were released, a reflection of West Ham's collective inexperience, but Davies insists the result was far from a foregone conclusion.
"I have to say we know Sam Allardyce has bigger fish to fry... we know he has injuries like ourselves but before the game we were concerned, because in Downing and Jarvis, Maiga and Morrison they had £20million of talent in the front four," said the Scot.
"I wish I had £20million worth of front players. But our play has been very good and we created a host of chances. I'm delighted with the way we played."
Davies confirmed after the match that captain Reid had signed a new two-and-a-half-year contract.