Reigning Olympic 400m champion LaShawn Merritt has pulled up injured with a tweaked hamstring in the Monaco Diamond League event.

Merritt was entering the final bend when he stopped suddenly and began holding his left hamstring. However, the American athlete believes that he will be fit to compete in the Olympics.

After the race, Merritt said: "I felt my hamstring shake. It felt almost like cramp.

"It feels tight but the fact I can still flex my leg is reassuring."

Merritt is only competing at the Olympics after he successfully overturned a two-year drugs ban, which was issued in 2010.