West Ham fans were furious with the club’s decision to offload the 22-year-old in an £18 million deal earlier this month.
Hammers captain Mark Noble also made it clear that he was unhappy with the sale, saying that he was ‘angry, gutted and sad’ following Diangana’s departure.
However, Sullivan admits Diangana’s sale was needed in order to bolster the club’s transfer funds, although he concedes that David Moyes is not guaranteed a new signing before the end of the window.
‘It was a decision made because we have eight wingers,’ Sullivan told talkSPORT.
‘Agents offer me players all the time and if they are wingers, I say ‘look we have got too many wingers’. We have some wonderful wingers who are not in the team.
‘Robert Snodgrass who played yesterday in a holding midfield role scored a wonderful goal. Anderson is a fantastic player, Yarmolenko had two assists last night. Unfortunately we have got a very unbalanced squad.
‘We now have the funds to buy a player or two. Unfortunately players the manager wants, we can’t get. We have two or three bids. Unfortunately the benchmark is very high, it is very hard to get those players.
‘I cannot say for sure we are going to sign anybody. As each day passes, I get more depressed.
‘We are not Roman Abramovich. We are not the owner of Abu Dhabi who owns Man City.
‘Even they have some sense now in value and they won’t overpay on what they value a player.
‘You can’t pay double what you value a player at. We haven’t got the money. The club will go bankrupt. These are difficult times and we have to be sensible.’
‘He doesn’t want to bring players in who, in his opinion, are just numbers, are just squad players. He wants to bring players in who will improve the team.
‘We have a number of bids in for a number of players, these are key players at decent size clubs, obviously outside the UK.
‘They don’t want to lose them so it is difficult. Whether we get any of these players, I do not know. Some are young, some are old.
‘What we need is wins. The way we played against Arsenal at the weekend, we are capable of winning games.’