England wicket-keeper batsman Jos Buttler admitted that he's not been "quite performing to the standards" he would want to in Test cricket and is working on improvement and a positive approach.

Buttler has so far featured in 38 Tests in which he's made 2,046 runs at an average of 33. In 2019, he played 11 Tests, scoring 502 runs at 25.10 and only crossed fifty thrice.

"I feel like I'm not quite performing to the standards I need to," Buttler said ahead of the New Year's Test against South Africa on Wednesday, 1 January. "I'm trying to improve that and affect games in positive ways for England."

Captain Faf du Plessis was delighted after 🇿🇦 registered their first Test win in 11 months, and has eyes set on bigger ambitions! #SAvENGhttps://t.co/blmEpkdgqu — ICC (@ICC) December 30, 2019

The 29-year-old made a Test comeback in 2018 after almost a year and a half, and registered impressive numbers with the bat that year. He scored 760 in 10 Tests at 44.70, including his only Test hundred.

"Since I've come back into Test cricket I've tried to trust my defense for longer periods of time," Buttler said. "I've been able to do that on occasions. But [playing my natural game] is certainly something I'm trying to work out.

"You can do a lot of work in the nets but I'm spending a lot of time thinking about the game when I'm in my room or trying to visualise things or work through them in my head. Moving forward I've got to play the situation, but I will try to be a bit more positive."

South Africa wicket-keeper batsman Quinton de Kock made a 95 and 37-ball 34 in the opening Test against England in Centurion, which the hosts won by 107 runs. De Kock played a vital role in the game and Buttler, looking up to his counterpart for inspiration, said watching the South African bat from behind the stumps "resonated" with him.

"Quinton played a really good knock and put pressure back on the bowlers," Buttler said. "He tried to take the initiative and, watching that from behind the stumps, it resonated with me.

"When you're batting with the tail, you try to sum up situations and work out how best you can score. You work out your risk management: what is too much risk; what is trying to push the game on. Looking ahead to this Test, I want to look to be a bit busier and try to look a bit more on the positive side."

The second Test starts on Friday, 3 January, in Newlands.