West Ham co-owners David Sullivan and David Gold were confronted by angry supporters after yesterday’s 2-0 FA Cup defeat at Wigan, according to Sky sources.
The supporters were angry West Ham have signed only Joao Mario - on loan from Inter - this month.
The club paid a £2m loan fee for the Portuguese midfielder and are paying his £100,000 a week wages.
And joint-chairman David Sullivan insists the club are working hard to make further acquisitions before the transfer window closes on Wednesday.
Sullivan told the West Ham website: "I have been made aware of reports suggesting that there will be no more players joining the club this month due to funding not being available.
"Nothing could be further from the truth.
"The manager David Moyes has the board's full backing in this window and, together, we continue to work night and day to bring in players to add quality and depth to the squad, despite January being a difficult time to do business.
"We are undefeated in our last five Premier League matches and are working round the clock with the manager to do all we can to ensure this run of good form continues."
Marko Arnautovic, Javier Hernandez, Joe Hart and Pablo Zabaleta all arrived at West Ham during last summer's transfer window.