Leadbitter said: "Who knows whether we will click together. You never know.
"As yet, we haven't trained together.
"But I hope to link up well with him, and he'll be a big addition to the squad."
Wayne Rooney has returned to Everton after 13 years at Manchester United.
Germany defender Antonio Rudiger has joined Chelsea from Roma on a five-year contract.
Wayne Rooney has returned to Everton after a record-breaking career at Manchester United.