The Proteas arrived in England with high hopes but have long been out of the race for semi-final qualification, having won just two out of eight matches heading into Saturday's group-stage finale against Australia.
The 34-year-old batsman, South Africa's captain in all formats since September 2017, admitted Friday he was approaching a key moment in his career.
"My plan for myself was to commit fully to the World Cup and not even think of anything else," du Plessis told reporters at Old Trafford.
"I didn't want my mind to start drifting into the future. I wanted to be completely present.
"Right now is possibly not the best time to be making decisions because you are disappointed. You don't want to be in this mode when you're making career decisions.
"It's a case of taking some time off and reflecting on what the future is like for me and what my purpose is going forward."
South Africa's next major assignment is a tour of India and du Plessis said: "I feel in terms of my own game, the last year is certainly the best I have ever played. There are no question marks there."
The weakness of the rand to other currencies has seen several players cut short their South Africa careers to play cricket on better financial terms elsewhere.
Some, such as Hampshire fast bowler Kyle Abbott have opted to play English county cricket under the 'Kolpak' ruling, which applies to countries such as South Africa that have trade agreements with the European Union.
Meanwhile outstanding batsman AB de Villiers has become a 'gun for hire' in the world's lucrative Twenty20 franchise leagues.
Asked if there was anything the International Cricket Council could do to stop the exodus, du Plessis replied: "The ICC certainly not. Cricket South Africa, I know they have been trying to put things into place.
"That will become the biggest issue for us to try and stay away from for all players and that's, you know, including myself."
Saturday's match comes 20 years after Australia and South Africa's stunning tied World Cup semi-final at Edgbaston that got down to the last over with the Proteas needing one to win and one wicket standing.
But a mix-up between Lance Klusener and Allan Donald saw the latter run out.
"You think Lance, who was seeing the ball big, could take down a boundary at any stage of that over," recalled du Plessis.
"But then you put yourself in that situation, it's not always as easy as it looks."