Morgan was forced off in the first period after picking up the problem following a challenge on Huddersfield's Steve Mounie.
“The bad thing today is we lost Wes [Morgan], I don't know how long for," said Puel. “It's a bad injury, a hamstring injury, he slipped on the pitch in the first half.
“With all the tiredness from the games and we can see a lot of injuries with all the teams. It is difficult.
“Jamie [Vardy] isn't long-term. He is not bad. He felt something against Liverpool and it was a precaution about him.
We will see for the next game – it's an important game for him in the cup. We will see. We will not take a risk, but it isn't a bad injury."