US Open champion Rory McIlroy says he remains "very close" to Andrew "Chubby" Chandler, the manager he surprisingly dropped last month after a four year association. The 22-year-old world number three, in an interview with the European Tour's official website on Wednesday, added that there was "nothing personal at all" in his decision that stunned golf. McIlroy split with Chandler's International Sports Management (ISM) firm to join Dublin-based Horizon. "It's a decision I didn't take lightly," McIlroy said ahead of this week's WGC-HSBC Champions in Shanghai. "I thought long and hard about it and had a lot of chats with my Mum and Dad. Sometimes to go forward in your career you just need to make decisions." McIlroy told Chandler he was leaving prior to last week's Shanghai Masters, where he then scooped the biggest first prize in the sport - £1.25million - after a play-off with American Anthony Kim. "For four years I felt Chubby was the best guy and ISM were fantastic for me, but sometimes to progress you need to have a fresh view on things. "It's about me trying to play my best golf and that's all there is to it. "I feel like a new environment around me it might enable me to play even better and I feel like I'm moving on to the next stage of my career. "Chubby's been there for me since day one and it was very difficult for me. I remain very close to him - it was a purely business decision and nothing personal at all. "I've got all the time in the world for Chubby and everyone involved at ISM." Last week's event did not count towards the European money list, but this week's world championship does and, with world number one Luke Donald pulling out to await the birth of his second daughter, McIlroy can cut his lead at the top from £1.12million to £404,000. McIlroy has the Hong Kong Open on December 1-4 and the following week's Dubai World Championship to come, but Donald will be back for the second of those.