Selkirk – who finished second bottom of the top flight table last term after winning six and losing 12 of their 18 league matches – go into the Marr match having won 31-21 at Jed-Forest in the teams’ BSPC Border League opener last weekend.
"It will be difficult,” Henderson told Borders Rugby TV. “We’ve got a whole group of players still here but then we’ve got some new ones coming in.
"It’s trying to gel everybody together, everybody knowing the calls. The attack structures have changed, the way we defend has changed.
"It’s about working really hard on the training park every week and boys starting to understand their roles and responsibilities. Each week it will come but the start of the league games comes pretty quickly.
"So we need to learn quickly. Our first premier league game will be very difficult.”
Last weekend’s Jed-Forest-Selkirk encounter saw the visitors open a 14-0 half-time lead via tries for Ross Nixon and Aaron McColm, both of which were converted by Hugo Alderson.
Jed hit back before half-time with a Grant Paxton try converted by Finn Scott.
Into the second half and Alderson converted his own score before further tries for Oliver McClymont and Andrew McColm rounded it off prior to a pair of late Jed tries for Clark Skeldon and Gregor Young converted by Scott.
Henderson acknowledged that his Selkirk squad is in a much better place than a year ago, when they were on the receiving end of a shock 53-19 loss to Biggar in their final pre-season friendly.
And he revealed that the Selkirk players have been putting in lengthy gym sessions during the off season.
"It’s been a hard pre-season,” he added. “The boys have worked really hard.
"We set up a gym programme for them not long after the season finished.
"They had maybe four or five weeks off then into the gym.
"So there was a lot of work getting done there. That’s been transferred into the sessions.
"You can see a difference in the physicality and the intensity in our pack and defence.
"It’s a better start in terms of games. I think it was 50 points Biggar put on us which was disappointing.
"However, there is a lot of evidence that what we’ve been doing over the last few weeks is working.”
Meanwhile, Jed-Forest – relegated from the Premiership last season after finishing bottom of the pile – will face the aforementioned Biggar away from home in their National League Division 1 opener this Saturday, with a 3pm kick-off at Hartreemill.
Jed head coach Stuart Johnson told the Southern Reporter: “Our defensive shape let us down against Selkirk. We gave away four soft tries unfortunately so we need to do work on our defensive shape.
"Biggar’s always a tough place to go. I’d rather go now than in December though.
"The pitch is small and has a bit of a slope to it as well.
"At least the pitch should be in good condition and there should be some grass on it.
"Biggar have got big physical forwards, they’ve got a good couple of backs and they’ve made a couple of decent signings over the summer.
"I know Reiss Cullen has joined them and Scott McClymont has joined from Selkirk in the forwards.
"Then you’ve got Andy Jardine who’s been there for a while who I know well from my Melrose days, Voas the big prop who’s been there for a long period.
"We need to match their physicality up front and play the conditions and the hill, especially going up the hill into the wind.”
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Selkirk head coach Gordon Henderson pictured last Saturday Photo: Grant Kinghorn
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Head coach Stuart Johnson with Jed-Forest troops Photo: Grant Kinghorn
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Selkirk's Corey Tait on the attack during last weekend's win Photo: Grant Kinghorn
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Try scorer Oliver McClymont on the ball for Selkirk Photo: Grant Kinghorn