Big Sam missed the win over Bolton on Sunday and he will also not be around for the game with Fulham at Craven Cottage on Wednesday night.
Sam is due for an angioplasty on Friday and that means he will also miss the home game with Stoke City the following day, but hopes are high that he will return for the Carling Cup quarter final against Chelsea.
McDonald said: "The procedure is on Friday and they are saying if everything goes according to plan then (he will be back) in the next couple of days.
"We are hoping he will be back for the Monday before the Chelsea game.
"He is a strong man. He does everything as he has to and if this week goes according to plan with another result against Fulham, it will take all the stress out and he will come back quickly.
"When you are talking about the heart and an operation it's always a concern but I think he has been reassured that it is routine."