Everton boss David Moyes refused to be drawn on the Brazilian Jo's long-term future at Goodison Park.
The striker scored twice in the 4-0 win over Wigan on Sunday.
But despite his double against Wigan taking him to five in seven games since moving to Everton, Moyes won't reveal if he is planning a permanent move.
He told the Daily Star: "Let's just say he is doing really well.
"I've seen him improve in training and his match fitness has got better."