Lallana signed for a big fee last summer but failed to really get going in a Liverpool shirt.
Lallana moved to Anfield last summer for around £25 million from Southampton, but has failed to hold down a place in the side - though he has shown glimpses of what he is capable of.
Henderson said it is a big season for Lallana as he looks to show why the club spent so much money on him.
He said to Liverpool's official website: "I felt a bit sorry for him last season but Adam is a top, top player.
"He’s got great quality and he’s got great knowledge of the game. He’s a good lad as well and I’m sure he will work really hard this pre-season and come the first game of the season I’m sure he will be flying. I’ve told him that I’m expecting big things from him this season!
"We see every day in training what he’s capable of. We saw glimpses of it last season but those injuries sort of knocked him off track a little bit, but I’ve told him this season is his season.
"It’s a big season for him, he knows that, but I’m sure he’s got more than enough ability and enough work rate to achieve that."
Lallana faces plenty of competition in his area of the side following the signing of Roberto Firmino from Hoffenheim this summer - while Philippe Coutinho, Jordon Ibe and Lazar Markovic are all likely to be competing for a place in that area of the side. Therefore, there is a great need for Lallana to deliver the goods both for his own good as well as the team's.
So for Lallana to play anywhere near regularly he is going to have to hit the ground running this season - but he has shown what he is capable of during pre-season with two very well taken goals against a Thailand XI and Brisbane Roar.
After the disappointing campaign last season where Liverpool only managed to finish sixth, and without a trophy to show for their efforts - there is a need for everybody to improve this season, which Henderson has acknowledged.
Greater contributions from every individual is going to be required if Liverpool are to get anywhere near the kind of form that led to them being shock challengers for the Premier League title in 2013/14.