Joe Root says Brendon McCullum is "one of the best coaches I've ever worked with" and insists his game has improved during the 44-year-old's England tenure.

McCullum's position has been under severe pressure following England's disappointing 4-1 defeat to Australia in the Ashes.

In the aftermath of the heavy series defeat, the England and Wales Cricket Board (ECB) said a review would begin, with the positions of those in leadership looked at.

While sporting director Rob Key is reportedly set to keep his job, McCullum remains in the spotlight, though Root is the latest England player – after Harry Brook and Ben Stokes – to throw his support behind the head coach.

"I think Baz is one of the best coaches I've ever worked with," Root said following England's win in the second ODI against Sri Lanka in Colombo.

"Obviously, we're disappointed with the way things went out in Australia, but I still think there's a lot more really exciting things to come from this group.

"If you look at my own personal game, the time that he's been the coach, it's improved tenfold."

Joe Root top-scores with 75 as ENGLAND WIN!

@IGcom pic.twitter.com/skwvBAuax4

— England Cricket (@englandcricket) January 24, 2026

Since McCullum took over in 2022, Root has become England's all-time leading Test run scorer (now up to 13,943) and has plundered 16 red-ball centuries in 46 appearances.

He also scored his first-ever tons in Australia during the recent series, ending his long wait for an away century in the Ashes with 138 in the second Test in Brisbane.

England also won their first away ODI match since November 2024 when they beat Sri Lanka on Saturday, while also earning a first win in the format under McCullum (previously lost 10 straight).

"Obviously, it's more fun when you win," Root said, addressing England's current dressing-room environment. "But I'm still having the best time of my life.

"I get to turn up and do the thing that I love every day with a great group of people, some brilliant minds and some experts that you can constantly keep improving and developing under."

England levelled the ODI series against Sri Lanka at 1-1, with the final match taking place on Tuesday.