LONDON, United Kingdom - Dave Lewis, the new chief executive of Tesco, the world's third-largest retailer, said further management changes at the troubled British grocer were inevitable.

The former Unilever executive and turnaround specialist started his new job on Monday - succeeding the ousted Philip Clarke a month earlier than planned - with a remit for a major review of the 95-year-old business which issued its second profit warning in two months last Friday.

"Will there be (management) changes? Let's be honest, there has to be. We don't want the trend of our business to carry on," said Lewis in a video posted by Tesco on YouTube.

"What the nature of those changes will be, you're just going to have to trust me for a while ... I won't be making decisions hastily but I will, if I need to, change things. I will make those calls."

Some analysts reckon UK managing director Chris Bush is particularly vulnerable given Tesco's underperformance in its key home market.

Lewis said he had "lots of ideas" and "lots of thoughts" about addressing Tesco's loss of market share in the UK but would not be jumping "to a very simple solution for that".

"I'm going to spend some time listening, I'm going to spend some time observing and learning from colleagues as to what it is they think we could be doing," he said.

"But I do think it's pretty clear: We have to get back to the core of our business ... We will go back to finding out what it is, be it price, be it service, be it availability, what it is that customers need from us so that they reward us with their loyalty."

Lewis also said he would not make any "knee jerk" decisions on pulling out of some of the 11 overseas markets Tesco operates in.

"I'm very happy with the business that we've got and we're going to run the business that we've got," he said.

"I've got some questions and I've got some things I need to learn and I need understand."

The new CEO said he recognised the strength of Tesco's brand had waned and that staff morale had suffered but called on the firm's 500,000 employees, 320,00 of which are in the UK, to focus on improving the customer experience.

"I think when we do that we'll be OK in terms of managing the commercial aspects of our business and therefore not needing to make some of the changes that some people outside of our business are advising us to," he said.