The Blues host London rivals Tottenham on Sunday knowing that the victory could put them top of the Premier League table.
Lampard will have to make a number of decisions about the showdown with Havertz and Christian Pulisic back in the competition.
Havertz, who signed Chelsea from Bayer Leverkusen last summer, has been out of action for nearly a month after testing positive for the coronavirus.
Meanwhile, US international Polisic has regained fitness after suffering an injury last month.
Despite the availability of Havertz, Merson says Chelsea should stick with the attacking players who have proven effective in recent weeks and leave the German international player on the bench.
Said a former Arsenal and England man StarsportChelsea: ‘found the right mix up front without Kai Havertz in the team and he may find himself on the sidelines now.
“It’s so competitive now that if you find yourself out of the team, it can be hard to get back into it.
Havertz missed a few matches because he tested positive for the coronavirus, and Chelsea won them all.
They’ve had Tammy Abraham up front and Timo Werner playing on a larger scale, and it suits them. It seemed to be the best system for them.
Havertz didn’t cut down any trees before missing those games. He is a young boy who needs time to settle down.
I wouldn’t put him up again against Tottenham because they look better without him now.
Tottenham did exactly what you thought against Manchester City and proved that they would be rivals. But I actually think Chelsea will test them more.
City was trying to score the perfect goal. Chelsea will be more direct and more speed. I don’t think Tottenham can have 35 per cent possession against them and win.
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