Staff at Charlton Athletic have expressed “extreme disappointment” after bonuses they say were promised to them by the owner, Roland Duchâtelet, were not paid, in the latest controversy of the Belgian’s tenure.

Administrative staff say they were due to be paid bonuses on 31 July but the money did not arrive. In an email to staff on Wednesday Duchâtelet said the “incentivised bonuses” would not be paid because the club had endured “a very bad financial year”. He did not take any responsibility for that poor performance.

In a statement, the unpaid staff said they would continue to work but it is clear that trust between the staff and owner has eroded. “We wish to express our extreme disappointment at your decision not to pay hard-working staff the money that had been previously promised based on our performances this year,” it read.

“The work produced by staff, who dedicate their lives and go above and beyond to do their best for Charlton Athletic football club, is dependent on a large amount of goodwill.

“Many members of staff willingly dedicate more time than is contractually necessary in what have been increasingly tough conditions because we take great pride in working for the club and its supporters.

“However, that goodwill has been seriously eroded by what we regard as severely unfair treatment of loyal staff whose hard work and dedication have not been rewarded as promised … the unanimous feeling amongst staff was that of anger and upset at both your decision and the lack of previous communication surrounding the money that we were due to be paid on Tuesday July 31st.

“As staff, we will continue to fulfil our contractual obligations to the best of our abilities, but we are also considering our next steps to ensure payment of the bonuses as promised.”

Duchâtelet, who has owned the club since 2014, is reportedly in the process of selling Charlton to an Australian consortium led by the businessman Andrew Muir. However, this has dragged on for some months.

The club have no permanent manager (Lee Bowyer has officially been caretaker since Karl Robinson left in March) and no formal chief executive since Katrien Meire moved to Sheffield Wednesday in January.

This summer it emerged that the club had stopped giving bottled water to youth players at their training ground, as one of a number of moves to cut costs.

A club statement in response to the bonuses matter said that “every employee has been paid on time, every month” and that “the club will continue to fulfil contractual obligations”.

The Guardian has attempted to contact Duchâtelet directly but he has yet to respond.