Everton are set to hand a debut to new goalkeeper Stefan Wessels for Saturday's big match against Manchester United.
But the joint is sore and painful, causing a headache for Everton manager David Moyes.
Howard, who signed a permanent five-year deal at Everton in February, said: "Right now it's swollen like a balloon.
"I'm hoping that the flight doesn't take too much out of it. I'll see the doctors when I get back. It is pretty sore. I just tried to play through it and hoped the adrenaline would get me through."