Leiston can make up ground on Ridgeons Premier leaders Dereham Town, according to manager Mark Morsley.
The Blues defeated Royston 1-0 in the second round of the FA Vase on Tuesday, but their cup exploits mean they have played eight games less than Dereham.
"It's a concern to us," Morsley told BBC Radio Suffolk.
"It's going to be tough because Dereham have got a head of steam but I'm confident come May next year we'll be there or thereabouts."
The Suffolk side, who will now host Hythe Town in the third round of the Vase on 4 December, are 19 points adrift of the table-toppers and will have to tackle a congested fixture list if they are to close the gap.
"Is my squad big enough for the league? I think it is," Morsley added.
It seems that sometimes we don't finish sides off as well as we should do but it's something we're working on
Leiston boss Mike Morsley
"We've brought a couple of players in, there might be one more coming into the building this week or early next week."
Leiston are in good form in the Ridgeons Premier and are on a run of 12 games without a defeat, but Morsley is looking for a killer instinct from his side.
"It seems that sometimes we don't finish sides off as well as we should do but it's something we're working on," he said.
"I haven't got a huge problem with it because we are still creating chances and when you're not creating chances it's a bigger problem."
Norwich United make the trip to Victory Road on Saturday, with Morsley likely to be without captain David Head (hamstring) and midfielder Stuart Boardley (groin).
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.