Pulisic suffered the injury during the warm-up ahead of the Blues' 3-0 Premier League win at Burnley on Saturday.
"Christian had a scan yesterday which showed a very minor injury to his hamstring," Lampard said in a pre-match media conference.
"He won't be fit for tomorrow, but we will see after that.
"It's obviously a relief for it to be on the small side. Christian made the right decision not to play in a game that could have made it worse. He's an important player for us.
"Some players who play on the edge and have speed could be more susceptible. We are looking at ways to manage Christian.
"We are all working in the same direction to try get him to be match fit as regularly as possible. We know the talent."
The United States international did not make his first appearance of the 2020-21 season until October because of a hamstring problem.
He scored in Chelsea's 4-0 win over Krasnodar last time out in the Champions League and has created two chances across five appearances in all competitions this season, though he has not been credited with an assist.
Defender Thiago Silva did not feature against Krasnodar but has played a pivotal role for a Chelsea backline that has kept five clean sheets across the Premier League and Champions League.
After the upcoming international break, Chelsea will play 12 games in the space of six weeks.
That packed schedule means Chelsea will likely have to rotate regularly, but Lampard insists managing the centre-back's workload is a simple task because of the Brazil international's professionalism.
"When you have an experienced player whose such a great professional like Thiago is, that honest conversation [about the workload] is very easy," he added.
"I'll be very upfront and honest with him about what I think and what he thinks."