Everton manager Ronald Koeman says it is still unclear whether Romelu Lukaku will be playing for the club next season.
But Koeman conceded that it can be "difficult" for clubs to keep their top performers.
Lukaku is the top scorer in the Premier League this season with 24 goals but has been linked with a move away in the summer.
Asked whether Everton might cash in on the striker, Koeman said: "I don't know. We will see what happens at the end of the season.
"We like to keep the best players but we know that it is difficult. I don't know if it is possible to keep them at the moment.
"Then we have to analyse the team, what we need to improve for next season.
"I think we need, offensive-wise, more players who score more goals, because the difference between Lukaku and the rest of the players is too big."
On Sunday Lukaku will come up against leaders Chelsea, who have been linked with a move for their former forward, although he failed to establish himself during his first stint at Stamford Bridge.
Seventh-placed Everton could clinch a spot in the Europa League this weekend, possibly without even kicking a ball if West Brom fail to beat Leicester on Saturday.
But Koeman wants to see more from his team after last week's 0-0 draw with West Ham.
"Maybe we need to change our mentality a bit because I felt a bit less intensity in the game last week, maybe a bit less motivation," he said.
"It is always difficult if you have already the seventh position in the pocket and maybe they get a little bit more holiday or end-of-season feeling.
"That is what I don't like. We like to keep momentum at home, we are strong at home, and we know what we need, to face the best team of the Premier League."