He has named an unchanged 21-man squad to the one that won 8-0 at Wigan Warriors in last week's elimination play-off.
Agar could name the same 17 but also has the option of recalling second-row Alex Mellor who has been out for the last nine weeks with a knee injury.
Others who hope to earn promotion to the matchday squad are Fiji prop King Vuniyayawa, Morgan Gannon - the 17-year-old second-row who has enjoyed a wonderful debut season - and utility back Jack Broadbent.
Asked today if he is pondering making any changes against the back-to-back champions, Agar said: "Yes, possibly.
"Not many. Not many at all. But possibly. We've had one or two selections dilemmas but we'll see tomorrow night
"We have considered the odd little tweak which is a good position to be in at this stage of the year.
"We're really confident with every guy in that 21.
"We'll look at that opposition and how we need to work through our bench rotations and see what's best for us but we have considered it."
The other semi-final sees sixth-placed Hull KR visit League Leaders' Shield winners Catalans Dragons.
Leeds, who came fifth, arguably have a tougher tie but Agar said: "I think both teams that finished one and two quite rightly have home semis and for different reasons both are difficult.
"Saints have won the comp' twice on the trot, are the Challenge Cup holders and conceded an average of just 11 and a half points per game.
"There's a shorter turnaround and the travel to France (for Hull KR) but from the experience of the last few seasons, Saints been clearly been the stand-out team.
"Both fixtures being their own challenges. Saints away is a tough tie but we're in a semi-final to get to a Grand Final and you wouldn't expect anything else.
"The positive we'll have is now we'll have a sizeable travelling away support which would have been difficult in Perpignan."
Champions Saints are seeking a third title in a row and Agar admitted: "Our defence has got to be bang on this week, as miserly as we were last week.
"Defensively we have to be as good as possible, our kick-chase as good as it has been all year and we need to get ready for a really tough, physical battle
"Saints' first 20/25 minutes is usually really very good and meeting fire with fire will be important for us.
"We're looking forward to it. We've prepped well and I feel we're ready."