Roberto Martinez has admitted that he was surprised to hear Everton fans boo him after withdrawing Muhamed Besic in Monday's 0-0 draw with West Bromwich Albion.

Boos rang around Goodison Park when Martinez replaced the impressive Bosnian with forward Arouna Kone for the final 10 minutes of last night's stalemate.

However, the Spaniard has hinted that his decision to sub Besic - a defensive midfielder - was linked to a potential injury.

"It did [surprise me] but I can understand the frustration around the crowd as well," he told the Liverpool Echo.

"Mo has to come off but then he wants to sprint off to allow Arouna to come on. I don't think it sends the right sign but it it is just part of the frustration."

Kevin Mirallas missed a first-half penalty as the Toffees extended their winless streak to six games in the Premier League.