England batsman Harry Brook said he was "living the dream" on the eve of his Test debut against South Africa.

Brook has replaced injured Yorkshire colleague Jonny Bairstow in the England team for the third and deciding Test, which starts at The Oval on Thursday.

The 23-year-old is the lone change to the side that levelled the series with a commanding victory in the second Test at Old Trafford after Bairstow was ruled out with a freak leg injury suffered playing golf.

"I'm taking every minute as it comes, not thinking about the outcome, how many runs I'm going to score or whatever," Brook told reporters on Wednesday.

"I'm just enjoying the moment. It's just another game, isn't it? I'm just hitting a ball. I'm already living the dream -- I'm looking forward to it."

Bairstow, in stellar form this year with 1,061 runs in 10 Tests, is a player Brook has long admired.

"I saw him yesterday (Tuesday)," said Brook. "I think he's down here (in London) seeing the specialist. He just said good luck and enjoy it.

"I've played quite a bit of cricket with him. I like the way he plays, smacking it around."

- 'Positive' -

Brook added his own attacking ethos would fit in well with the aggressive style England have developed while winning five out of six Tests under their new leadership duo of captain Ben Stokes and coach Brendon McCullum.

"I am going to try to be positive and put the bowler under pressure," he said. "I'm not just out there to survive. I'm there to score."

Brook has played four Twenty20 internationals for England and last month made 140 for the second-string England Lions in a tour match against South Africa at Canterbury but has not seen much red-ball action since.

"I played the Lions game, so it's not too bad," he said. "I'm still hitting a ball.

"I don't think the way I play changes too much. A little bit more extravagant in white ball, but like I say I am still trying to put pressure on the bowlers."

The Lions won by an innings and 56 runs, but South Africa did not field frontline quicks Kagiso Rabada, Anrich Nortje and Lungi Ngidi.

"He (Brook) got a few runs against us but, again, this is Test cricket and we've got our fast bowlers now who didn't bowl against him in Kent, so I'm not reading too much into that," said South Africa captain Dean Elgar.

"I just know the environment and this is the big league now."

Stokes, speaking earlier Wednesday, said of Brook: "The way in which our middle order has been playing this summer, I feel as if Harry coming in, the way he goes about his game with the bat is pretty much a like-for-like replacement.

"He's always going to look to take the bowling on, take the positive option. It's obviously devastating to not have Jonny but I'm very excited we get a replacement with the skill Jonny possesses."

South Africa won the first Test at Lord's by an innings and 12 runs, only for England to bounce back to win by an innings and 85 runs in Manchester.