Injuries had prevented Keita from hitting the ground running in the first few months of the season after joining from RB Leipzig, while former Monaco star Fabinho has only recently come into the Liverpool team after taking time to adapt to a new set of demands.
"I thought he started really well and then got an injury which set him back a little bit," Henderson is quoted as saying by the Liverpool Echo, as he spoke of Keita's Anfield career so far.
Describing Keita as 'outstanding' in this week's win over Burnley, the skipper added, "You can see how good he is on the ball, how comfortable he is; driving with the ball forward, which is important for us. I think he'll go from strength to strength as he gets more games and experience.
"But I think you can already see he's a fantastic player."
As for Fabinho, Henderson commented, "I think everyone makes it easy for people to come in and settle. But it's going to take time when you come in from a different league. He's doing well.
"I don't know whether he understands me! He's got lads around him, the Brazilian lads and the French lads. We're all one group and you can see that on the pitch."
Liverpool ensured that they kept pace with reigning champions and Premier League leaders Manchester City with a 3-1 victory over Burnley on Wednesday. Just two points separate the Reds from the Sky Blues, while there is a six-point cushion back to third place Tottenham.