Seidl started working at the Woking outfit earlier this year as its team principal, leading McLaren through a positive year, as it currently sits fourth in the constructors' championship.
Sainz says that Seidl is still warming into the team, but has hailed the German's impact at the team in the short space of time he has held his role.
"I think Andreas at the moment is still arriving at the team," Sainz said. "He manoeuvres such a big ship that you need to give him time.
"At the moment, what he has given us is a very clear direction of how he would like the team to operate, how he would like the drivers to be treated and how the drivers should treat the rest of the team.
"He's referenced what is a successful team, what does he think of a successful team and how do we want to become a successful team.
"Apart from that, he's had a lot of work to do in the factory to meet a lot of people and find out what are the weaknesses and strengths back at the factory."
McLaren endured a handful of difficult years, languishing towards the year of the field throughout the V6 hybrid era.
Seidl's appointment was one of the steps the team has taken in the hope of reviving itself towards the front of the field - but Sainz such an achievement will take 'years'.
"To start seeing results, we're going to need years, long periods of time to see his work ethic have an impact. But I can tell you from the driver side, he's already a big step forward and he's having the right impact within the team."
Bahrain International Circuit - Winter testing