"Yerry's a muscle injury, his quad," Lampard told evertontv. “Demarai was a hip. We are hoping with him it's not too bad. It's something that he's had before that he got over quite quickly but, with Yerry, we'll have to assess him over the next few days."
With Everton starting to dominate the game prior to the enforced changes, Lampard conceded their absences did not help his side's cause.
“They are two big players for us," he added. “Demarai's had a fantastic season so far and I thought that we were causing them some problems with Anthony [Gordon], Demarai and Richarlison as we wanted to.
“Yerry is obviously a big player for us as well, so when you lose two big players you also restrict yourself on subs in the second half.
"I would have made more changes to try to affect the game, but it was impossible to other than to bring on Donny [Van de Beek] who came on at a difficult time. They were big circumstances that happened that made it difficult tonight."