Faf du Plessis avoided questions over his South Africa future and urged his side to stay fully focused on winning the final Test against England.

South Africa are 2-1 down heading into the fourth and final contest in Johannesburg, with Du Plessis having already been replaced as ODI captain by Quinton de Kock ahead of the one-day and Twenty20 matches against 50-over world champions England.

Du Plessis has also hinted the match at the Wanderers could prove to be his last in red-ball cricket on home soil, revealing he may quit after facing West Indies in July and August.

However, Du Plessis did not entertain queries over his plans, instead focusing on the Proteas' chances of salvaging a draw from the series.

"I'd like to, for my own personal reasons, have my focus specifically on this Test match," Du Plessis told reporters.

"I know there has been a lot spoken about all the other things and too much noise away from Test cricket and the Test team. I would like to speak about what is in front of us.

"This is about this Test match for me. I have not changed communication to you guys in one instant.

"I've said the same thing but the question keeps coming up. I am still committed to playing for South Africa. That hasn't changed. It's normal business as usual."

Du Plessis does not believe South Africa can dedicate any more practice to improving technically, but rather asked his team to display a new mindset.

"When you are deep in the series already, the extra time in the nets is not going to make that much difference," Du Plessis said.

"The challenge is how mentally strong we are. There's not enough time to change techniques. The secret weapon lies in how strong we can be emotionally and mentally.

"If you are mentally off it, teams that are on top of you just keep running with that momentum. But we know England are not going to say, 'here you go guys here's five or six wickets in this next session, let's play now', we have to earn it."