Hamburg, who have been beaten in their last seven games in all competitions, are in danger of losing their proud record as the only ever-present team in the Bundesliga's 51-year history.
Hamburg are second-bottom a point behind Nuremberg, who occupy the relegation playoff spot, and on Saturday visit basement side Eintracht Braunschweig who are four points adrift.
"Unfortunately, too many of the old guard still prevail and are not interested in an honest new start," former West Germany international Magath said on his Facebook page.
"Parts of the advisory board, the management board and the HSVplus group have turned against me. How can you successfully lead a team through a relegation battle in such conditions?"
The HSVplus group was formed to look into setting up a new structure where the professional football team would be separated from the rest of the club and converted into a joint stock company, opening the way for investors.
SHAMBOLIC DISPLAY
Hamburg SV's plight took a turn for the worse when they lost 3-0 at home to Hertha Berlin in the Bundesliga last Saturday after a shambolic first-half display.
A group of fans waited outside the players' entrance after the game, insulted them and damaged vehicles.
Although chief executive Carl Jarchow backed van Marwijk, the club's 11-man advisory board met on Sunday to discuss the future of both men.
However, an eight-hour meeting failed to reach agreement and the board members left the hotel by a back entrance.
On Tuesday, German media speculated that the board was on the point of voting in favour of Magath who could even take over before Wednesday's German Cup quarter-final at home to Bayern Munich.
In the event, nothing more happened but the situation took another turn for the worse when Hamburg produced another pitiful display and lost 5-0 to the holders.
Hamburg are one of the few Bundesliga clubs who still use the traditional structure of an 11-man advisory board which in turn picks a four-man board of directors.
The advisory board wields considerable influence but is made up of people from all walks of life and is elected by the club's members.
"Nothing can succeed without unity in the club," said Magath, who won two Bundesliga titles as manager of Bayern Munich and another with VfL Wolfsburg.
"It does not seem feasible to install this unity with all these vast groups and individual interests."
(Writing by Brian Homewood in Berne; Editing by Ken Ferris)
