Phil Mickelson says his former caddie John 'Bones' Mackay is irreplaceable and the respect between the both of them is immense.

Mickelson confirmed the split from 'Bones' two weeks ago, ending a remarkable 25-year partnership, and the former world number two instead goes into this week's Greenbrier Classic with brother Tim on the bag.

With Mackay by his side, the American won five Major titles, 41 PGA Tour titles, triumphed nine times on the European circuit and only just missed out on becoming world number one due to the dominance of Tiger Woods over the years.

It will be a different feeling for the 47-year-old without his usual caddie on the bag but 'Lefty', who was full of respect for 'Bones', is confident his sibling can help him along the way.

"I'm hesitant to talk too much about anything because I'm so appreciative of the time I have had with 'Bones' for 25 years that anything I say positively about what I'm looking forward to with Tim and so forth I feel would be taken as a shot at Bones," Mickelson said. "I don't want to do that.

"I have too much respect for him and our time together over the years. The thing I would say is Tim is one of my favorite people. I love being around him. He's one of the people I respect the most, and throughout my career he's been so supportive of me. We've never had that kind of brotherly rivalry growing up.

"We're seven years apart. We've done nothing but support for each other throughout our lives. To have that type of friendship with my brother is something I really value, and this time together. But there is no replacing Bones."