Boss Roberto Martinez is keen to retain the services of Lukaku after a successful spell on loan at Goodison Park last season when he scored 15 league goals in 31 appearances.
But Everton would need to sign him on a permanent deal to loan Ghana winger Atsu, because they are not allowed two players on loan from the same Premier League club.
Bundesliga side Wolfsburg and Italian champions Juventus have also been linked with a £20m bid for Belgium international Lukaku, who has yet to score for Chelsea since his 2011 move from Anderlecht.
He is expected to join up with the Blues in Holland this week ahead of Wednesday's friendly with Vitesse Arnhem, when coach Jose Mourinho will have a closer look at the 21-year-old and make a decision on his future.
And assistant first-team coach Steve Holland said last week he is not expecting any movement on Lukaku before August.
On Saturday afternoon Sky Bet suspended betting on Lukaku's next club after a string of bets on Wolfsburg.