Chelsea's interest in defender John Stones has destabilised the youngster, said Everton boss Roberto Martinez.
The Blues made two official offers - £20m and £26m - to sign the Englishman, both of which have been rejected by the Toffees.
And Martinez says the 21-year-old was affected by the interest shown in him by the Premier League champions.
"Yes [it has affected him] and you hope you learn from it and become more mature," Martinez is quoted as saying by Metro.
"Clearly, John is one of the outstanding young talents we have in the squad and you are going to get interest. That is a positive.
"Our focus is on Watford this weekend. John is an Everton player."