The key pair were absent as the Toffees picked up their first pre-season victory of the summer - a 4-2 win at Blackpool on Sunday.
Calvert-Lewin and Gray both suffered minor issues after returning from Everton's tour of America and were not risked.
And with the duo set to train in the coming days, it bodes well for their chances to face Thomas Tuchel's side at Goodison Park.
What’s been said
Speaking to Everton's club website, manager Lampard said: "You're concerned because you want them on the pitch but they're small issues that were not worth risking
“We travelled back from America which is a long overnight flight back from Minnesota.
“Then the lads needed a bit of time off and have got small issues.
“Hopefully, they will be fit to train by the middle of the week and we'll play it from there.”
Seamus Coleman was again missing against Blackpool after undergoing an operation during the off-season.
Andre Gomes was also absent, although Allan returned from a setback to feature off the bench.