Gerrard suffered a hamstring injury in Saturday's 4-1 Premier League home win over West Ham, ruling him out of Sunday's visit to Tottenham - and it may also keep him out over the busy Christmas period.
Brendan Rodgers' squad is already stretched, with striker Daniel Sturridge out with an ankle strain until mid-January and Jose Enrique still missing after knee surgery.
"Any team without Stevie is going to miss him, clearly," said Johnson.
"We have got a good squad and hopefully that (Gerrard's injury) is not as bad as it looks."
Liverpool are currently second in the Premier League table but Johnson says he is still not entertaining thoughts of a title challenge.
"Personally I don't look at that. It is in the back of your mind but if we keep picking up points, we don't have to worry about that, it will take care of itself," he added.
"But we are good enough to be up there.
"We have some tough away games coming up. We only worry about the next one and I am sure we will step it up for the so-called bigger teams."
Liverpool boss Rodgers has confirmed Gerrard will be assessed this week to see how serious the injury is.
"It was his hamstring so we just need to see how it is," said Rodgers. "He was outstanding in his performance, the quality of his passing, but when he went to get that pass he felt a little tweak.
"We just need to assess that in the next day or so. It was definitely his hamstring. Hopefully it's just a strain and we'll see where we're at in the next 48 hours."
Rodgers also revealed that Daniel Agger missed the game against West Ham through illness, but he was happy with his replacement Mamadou Sakho after the Frenchman scored his first goal for the club in the 4-1 victory at Anfield.
"Daniel felt sick this morning when we arrived at the training ground," added Rodgers. "But a more than capable replacement came in, who I thought was excellent.
"I thought Sakho looked strong and aggressive and he looked like he really wanted to take his opportunity. He did that. I thought he and Skrtel were both excellent."