Opener Alex Hales is in a "good place" despite mounting pressure to prove he deserves his Test spot, according to England and Nottinghamshire team-mate James Taylor.
Hales, 27, has opened the batting on the tour to South Africa, but averages just 20 from six Test innings.
He scored 60 in the drawn second Test but has only managed more than 20 on one other occasion.
"He obviously hasn't scored as many runs as he wanted," Taylor said.
"But I think he is actually in a really good place. I know him well and I know when he is down and when he is on a high."
Hales only scored 18 in his last innings, but it was his battling knock that helped set the platform for a comprehensive win and secured a series victory with one Test still to play.
Taylor, whose only half-century in the series came in the opening Test, but took two brilliant catches in the third Test, added: "He is desperate to score runs and keep contributing.
"He spent some time at the crease at the Wanderers in the last innings; it was a tricky time to bat and he got us in to a position to win the game. All that time at the crease will add up and hopefully he can go big in Centurion."
England's second opening place has become a headache for the selectors, with captain Cook having eight different partners since Andrew Strauss retired in 2012.
The fourth Test gets under way on Friday.