European 1500 metres champion Reyes Estevez faces a race against time to be fit for the World Championships in athletics in August, the Spanish runner said on Wednesday.
One of the host nation's main hopes for a gold medal, Estevez pulled a calf muscle at a minor meeting two weeks ago.
"The injury is a lot better now but I am very unhappy because, although I am now running, things are still happening very slowly," Estevez said.
The athlete had pencilled in the Golden League meeting in Rome on July 7 as his return to racing.
"But now I am not sure," he said. "I am going to talk to my coach and maybe it will be better to carry on training. The only meeting that matters this year is Seville and I am aiming to be 100 per cent there."
Estevez is expected to be the main challenger to Morocco's Hicham El Guerrouj, the 1500 metres world champion and world record holder.
Reuters for the IAAF