Downs face a jam-packed schedule in September following their progression to the Champions League semi-final, as well as the MTN8 semi-final.
The club earlier requested the league's backing to have their midweek fixture against Maritzburgh United on September 14 moved in order to prepare for their clash against Zesco United in Zambia on September 17.
However, the PSL have since added their MTN8 semi-final second leg three days before they're meant to face Zesco United at home in their Champions League return leg.
“We received communications from Sundowns asking for postponement and the league has written back citing our reasons for not being able to grant the postponements," said PSL spokesman Lux September.
"We have wished them the best of luck for they are representing the country."
The reasons, however, have not been made public and could cause claims of favouritism after Orlando Pirates were accomodated en route the 2013 Champions League final as well as the 2015 CAF Confederation Cup final.
Sundowns will now play five games accross three different competitions in the space of 14 days.
September 11 – MTN8 SF1: Chippa United vs Mamelodi Sundowns (Nelson Mandela Bay Stadium)
September 14 – Absa Prem: Maritzburg United vs Mamelodi Sundowns (Harry Gwala Stadium)