The Jamaican world record holder missed most of 2014 with injury and American rival Justin Gatlin went unbeaten in the sprints.
But Bolt said he was not worried about Gatlin, whom his coach already has declared no match for the six-time gold medal winner.
"He knows exactly what he is doing, so I don't doubt anything my coach says," Bolt told reporters in Rio, where he will compete in a challenge race on Sunday.
"When it comes to rivals there are seven people beside me in the lanes that count. When I am in great shape, I tell you guys, I worry about nobody.
"When I am at my best it is definitely almost impossible to beat me so all I need to do is be at my best and I'll be OK."
Gatlin, the 2004 Olympic 100m champion, finished third behind Bolt in London after returning from a four-year drug ban and last year recorded personal best times of 9.77 and 19.68 seconds over the 100m and 200m respectively.
Bolt's world records in the events are 9.58 and 19.19 seconds, both in 2009.
Track fans are looking forward to a potential showdown between the pair in August's world championships in Beijing but Bolt gave no hint he would face Gatlin before then.
"I don't know (if that will happen)," he said. "I think it is early in the season. I never run from a challenge. For me that would be fine, it is always good to compete with your best competitors to see where you stand. If it gets to that point... but right now it is way too early to say."
The laid-back Jamaican appeared more concerned about his fitness, three times saying it was important to have an injury free 2015 in order to have a smooth transition into what will be his final Olympics.
"We've been taking it slow and not trying to rush anything, I am working on my weaknesses just to get stronger," Bolt said. "The key this season is to try and stay injury free."
Bolt won gold in the 100m, 200m and 4x100m relay at the 2008 and 2012 Olympics. He plans to retire from athletics after the 2017 world championships in London.
(Reporting by Andrew Downie, editing by Gene Cherry)
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