DANI VALLVERDU has played down talk of a rift with Andy Murray, insisting the end of their working partnership was "genuinely mutual".

Murray made a host of changes to his group last season, hiring Amelie Mauresmo as coach to replace Ivan Lendl, who left his post in March and then stopping working with long-time friend Vallverdu and fitness trainer Jez Green.

The exit of Vallverdu raised some eyebrows as the pair met at the Sanchez-Casal Academy in Spain more than a decade ago, and the Venezuelan held an increasingly important role in the coaching team under Lendl.

Earlier this month, Murray appeared to suggest that the relationship had become strained, saying: "The most important point in any team is that everyone has the same vision, everyone wants to move forward together. Maybe the last four or five months of last year it wasn't like that."

But Vallverdu, who is now coaching Tomas Berdych, insists that was not the case and that the relationship had simply run its course.

"We were all pulling in the same direction," he said. "I'm quite proud of how we pulled it around after the US Open. It was pretty hard, him qualifying for (the ATP Tour Finals in) London from his position after New York.

"Of course, Andy is the one who played the matches, but everyone had the goal of helping him get there. I don't think the last four months are a reason we aren't working together any more, it was genuinely mutual.

"His determination, professionalism and stubbornness, that's what has made him so successful but, because of the way he is, it gets to the point when it is time for both parties to go their own ways."

He added: "Andy and I have been friends for nearly 15 years. Our personal relationship is still good, I consider him one of my best friends and I'll always be in his corner, except for when I am coaching against him."

Murray, meanwhile, will meet Bulgarian Grigor Dimitrov in the last 16 of the Australian Open tomorrow following his 6-1, 6-1, 7-5 victory over Portugal's Joao Sousa.

And a major obstacle to his progress to the title was removed when prospective quarter-final opponent - 17-time grand slam winner Roger Federer - was beaten 6-4, 7-6 (7/5), 4-6, 7-6 (7/5), by Italian Andreas Seppi.

"I just saw it, the match point, when I went out to cool down," said Murray, who lost to Federer in the last eight 12 months ago. "It's obviously surprising, but upsets happen in sport daily.

"It's just something that maybe because of the consistency of some of the guys in tennis people make a huge thing of it. But in sport in general it happens all the time, and pretty much on a daily basis.

"I don't know if Roger played badly or if Seppi played unbelievable. But if Roger was not playing so well, it's quite easy to lose at this level."

Murray knows that from bitter experience of Dimitrov, who ended the Scot's reign as Wimbledon champion in the quarter-finals last year.

"It will be a tough match obviously," added Murray. "He's played well in the slams the last year or so.

"He's obviously a talented player. He's one of the young guys trying to make a breakthrough, so he'll be motivated. Hopefully I can play a good match and make it tough for him."