Avram Grant has warned any prospective West Ham United manager that he faces being undermined by the club's owners, David Gold and David Sullivan, and also claimed that six different managers were offered his job as recently as January.

Grant has revealed to close friends the extent of his disillusionment during a season that ended in relegation and says he wishes he had never taken the Upton Park job. Grant was sacked on Sunday, immediately after the team went down.

"Avram points to January when Martin O'Neill was offered his job [when Grant was reportedly going to be sacked whatever the result against Arsenal on 15 January]," said a close friend. "He says six managers were asked by the club to take over, including Steve McClaren and Sam Allardyce, but they would not do it because they knew the situation there."

Grant is also disappointed that he was not allowed to take on the challenge of trying to return West Ham to the Premier League. "Avram feels frustrated. If he had not been sacked he believes he could have steadied the club and taken it on to much better things next season," the friend added.

"He actually said that despite all the financial difficulties at Portsmouth, where players were not being paid and the club faced liquidation, that job was far easier than the West Ham one because he could concentrate on the on-field job."

In a stark warning to potential successors, a list that is now headed by Chris Hughton, Cardiff City's Dave Jones and Ian Holloway of Blackpool, Grant told a confidant of several "red lights" that warned him just how difficult the job would be due to a lack of finance for players. "Avram was advised not to take the job by several people in football but he wanted the challenge," said a source close to the Israeli. "He feels almost from the moment he took over the situation was virtually impossible. One example is that he was concerned about the lack of a strong midfield-enforcer type when he arrived so he wanted to sign Marc Wilson, who was a player for him at Portsmouth.

"Wilson wanted to sign for Avram and Portsmouth would have sold him for £3m but the owners would not go beyond £2.5m and so he ended up joining Stoke [City].

"Another example is Yakubu [Ayegbeni, the Everton striker]. West Ham were willing to pay £6m for him – David Moyes [Everton's manager] wanted £10m so the deal could not happen, but Avram was not allowed to spend [that] money on other signings, which he could not understand.

"He regrets not checking out the club properly to find out the true situation about the budget. His vision was for the club was to be a mini-Arsenal, developing their own players and style. He knew it would be difficult in the first season, fighting relegation at the same time. But if he knew then what he knows now he probably would not have accepted the job."

Although West Ham would not comment on the record, privately the club point to players that Grant was able to sign. The New Zealander Winston Reid was bought for £3m in August while Sullivan and Gold also sanctioned the signing of Pablo Barrera for £4m and Thomas Hitzlsperger arrived on a free transfer.

In January Wayne Bridge and Robbie Keane were also signed, on loan from Manchester City and Tottenham Hotspur respectively, with West Ham paying the majority of each player's sizeable salary.

Tzofit Grant, the manager's wife, told the Guardian: "Maybe there was a mistake on Avram's part to accept the job. There were so many people who were offered it but turned it down because they thought they wouldn't be able to manage. But Avram wanted to rise to the challenge. There are so many things that we can't talk about – so many things he had to deal with that people don't know about. He found no joy except only with the fans, players and his assistants."