Roberto Martinez's team were leading 1-0 when Oviedo collapsed in agony after a first half challenge on Stevenage's Simon Heslop.

The Costa Rica international needed lengthy treatment from medical staff before eventually being stretchered off.

Everton team-mates Leighton Baines and Kevin Mirallas were visibly distressed after going over to check on Oviedo.

Leon Osman came on to replace the 23-year-old, who was immediately taken to hospital in an ambulance.

A message posted on Everton's official Twitter feed early in the second half of the Cup tie read: "Update on Bryan -- he's been taken to hospital with a suspected broken leg. Get well soon, Oviedo Baby!"

Oviedo's Everton team-mate Darron Gibson, currently sidelined by a knee injury, also tweeted: "Really feel for Bryan there, looked like a bad one!"

If Oviedo's injury is as bad as feared, he will face a race against time to recover for the World Cup in Brazil, where Costa Rica face England, Italy and Uruguay in the group stage.