MONACO - Usain Bolt says he is over his early-season setbacks and running into form at the right time to sign off his career with two more gold medals at next month's World Athletics Championships in London.

Bolt labored to a 10.06 winning time in the 100m in the Czech Republic last month and immediately traveled to see his doctor, Hans-Wilhelm Mueller-Wohlfahrt, for treatment on the back issues that have troubled him for years.

The Jamaican world-record holder will test his treated back in Friday's Diamond League meet in Monaco, which will be his last outing before he defends his 100m title and then runs in the 4x100m relay at the world championships.

"I'm feeling good," Bolt told a Monaco news conference on Wednesday, before explaining how the death of his close friend and former British high jumper Germaine Mason in an April motorcycle accident had hampered his progress.

"The season started off slow for me. I had a setback after my friend Germaine passed away. It kind of set me back a little bit," Bolt said.

"I had some work to do so I've been a little behind schedule, but I'm training well.

"I'm feeling much better over the last couple of days because I went to see my doctor in Germany and I've been training good, so that's a good sign, the weather's great here so hopefully on Friday it will be the same and I can perform at my best."

Bolt is unlikely to ever again match his best - the world record of 9.58 he set in 2009 - and the 30-year-old said he would be happy with any sub-10-second time as he seeks to find the speed he knows he'll need on Aug 5.

"It's just all about execution now, going out there trying not to worry too much about time," he said.

"It would be good to dip under 10 seconds, which will always help the confidence."

Bolt, with eight Olympic and 11 world championship gold medals and a host of world records to his name, said the time was right to retire, having achieved all his goals.

He laughed off the suggestion that he was running scared of Wayde van Niekerk and said he regretted that he was walking away just as the South African 400m and - as of last month - 300m world-record holder was becoming the sport's newest star.

Bolt is looking to bring down the curtain on his glittering career in style at the August 4-13 worlds.

"My main aim is just to win in London. I just want to retire on a winning note," Bolt said.

He revealed he would not defend his 200m world title, meaning he will not race against Van Niekerk, the athlete Bolt has tipped to take over as the next track-and-field superstar.

"I think that's one of the most disappointing things in my career now," said Bolt.

"He came along at this late stage and I didn't get to compete against him, because I think he's one of the best now."

Bolt was adamant there was little chance he would race again after the world championships but admitted he would likely stay involved with athletics.

"I've done everything that I possibly can in this sport," he said.

Reuters - Afp