Speaking after victory over Chelsea, Howe says injuries have worked against their ambitions this season.
Sunday's win strengthened Newcastle's hold on third place and Howe said afterwards: "I think we are missing some big players. Whenever you do that there's a gap. The lads that came in today filled that gap.
"I think the lads who came in today filled that gap superbly.
"That's par for the course from my perspective, you are looking for people to step up and show their qualities. That's bringing in players like Sven Botman and Anthony Gordon into the team - top class players and I think they both played well.
"Below that of course we are slightly stretched and we need to bring some players back.
"Of course, the summer window is there as we know, and I have made no hiding of the fact we need more."