Usain Bolt has warned his rivals he remains the man to beat at the world championships in London, despite what he called a “horrifying” start to his season and some impressive performances from his younger opponents.

Bolt watched with interest as the Olympic 100m bronze medallist, Andre De Grasse, ran a wind-assisted 9.69sec in Stockholm last week but laughed at a question about whether he thought he could still keep up with the 22-year-old. “Well, I am the fastest man in the world, so I will say yes to that,” he replied.

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De Grasse was helped by a illegal wind of +4.8 metres per second – a time that converts to 9.88 with zero wind, or 9.79 with a legal 2.0 wind – and Bolt also pondered why he never got a similar assistance during his career. “Every time I hear a wind-assisted time my friend NJ always calls me and says: ‘Why are we never this lucky, because we always have a negative wind.’ We have always thought about it. I’ve never been that lucky.”

Bolt, who is running in the Golden Spike meeting in Ostrava on Wednesday, admitted he had struggled to handle the emotions of competing in Jamaica for the last time when he ran a modest 10.03sec in his race of the season a fortnight ago. “I always get nervous for my first race but I was really nervous just with the energy and the amount of people there. The only time I have seen the stadium full like that was the girls and boys’ champs so it was emotional to come out and be there in front of my parents and best friends, it was something different.

“Race wise it was horrifying. It was really bad. I didn’t feel smooth as I should have. Bad start. Everything was just not perfect. But over time I will feel good and get better. And I think with running two more races for the championships [in Ostrava and Monaco] I will be fine.”

Bolt also had a few words for his old rival Justin Gatlin, who won the 100m at the US trials at the weekend to qualify for the world championships, which begin on 5 August. “I was actually shocked he won the trials,” he said. “I knew he would be in the top three but I was shocked he came out victorious. It just shows he is a competitor. He shows year after year that he is not to be taken lightly. I am looking forward to that competition always.”

Meanwhile Laura Muir’s coach Andy Young has insisted that she still intends to attempt an audacious 1,500m and 5,000m medal double at the World Championships despite reports that she was going to drop the 5,000m in London after suffering a setback due a foot injury.

At the weekend British Athletics performance director Neil Black had warned that the 24-year-old had only a “one percent’ chance of doubling up in London. But speaking to the Guardian, Young insisted that despite missing a fortnight’s worth of running due to a healing intracortical stress fracture of the second metatarsal, Muir’s training since coming back had gone far better than he had dared to expected.

Young said: “It appears that this had happened a number of weeks if not months previously, but as Laura had been training normally and without pain we had not realised. After initial scan result on 1 June it was decided as a precaution to stop weight bearing running until a more detailed scan and consultations.

“Laura resumed running on 16 June, pain free, and at her normal pace of 5.40sec and 5.50sec per mile. And the following week returned to the track, which likewise immediately was straight back on a world class pace. This past Saturday she completed 15x300m with 45sec recovery in 47-49sec per rep.

“As a precaution it is unlikely she will run the 5,000m at the trials this weekend, but with such a short lay off and training progressing so well she should be able to compete for a medal in the 5,000m as well as the 1500m in London.

“While it is a source of frustration for Laura missing the UK Champs this weekend, an event she particularly enjoys, fortunately she already has the qualifying time for London with her 14:49.12 she ran while breaking the British Indoor record earlier this year.

“Laura will run around four more races in July ahead of the world champs, and with training going so well the first of them will now be a few days ahead of the Muller Anniversary Games, at the Lausanne Diamond League, before attempting to break Zola Budd’s British mile record in front of a home crowd in the Olympic Stadium.”