The Belgian joined West Bromwich Albion on loan from Chelsea last season and went on to score 17 goals in the Premier League.
"The player did extremely well last season and has continued to do well for Everton," the Portuguese coach told reporters.
"The potential is there. We all recognise he can become an influential striker in the future.
"Chelsea's standards are very, very high so the jump will be very difficult for him, but he has shown he can cope with the Premier League and it's another step up for him, at Everton."
Lukaku moved to Stamford Bridge from Anderlecht in 2011 for a reported £18m fee.