Eastmond has not played a match since leaving Leicester last July and it is nine years since his last appearance in rugby league for St Helens, so Agar is keen to temper expectations.
Agar said: “The message is to keep it simple for starters. I certainly think he’ll help us in an area we struggled in last week, our last-tackle plays.
“We’ll tell him to feel his way back in. Clearly there’s going to be a lot of eyeballs on him and a lot of expectation but we’re very relaxed and understanding of where he’s at at this moment in time and also where we’re at as a team with a lot of key personnel missing.
“It will be up to the rest of the guys to help him around the field tomorrow in what is going to be the first game of rugby league he’s played in nine years.”
With skipper Luke Gale missing through injury, along with Richie Myler and Robert Lui, Agar will be hoping Eastmond can quickly plug the gaps in the halves.
Agar added: “To throw him straight in there in a pivot position is a real challenge for him.
“As coaches, we are being very pragmatic and understanding and want to ease him in but, at the same time, we’re excited about getting him up to speed as quick as we can so he can showcase his talents.”