How do your rabbits poops look normally? Are they normally irregular sizes and shaped, or are they the normal round ones and all about the same size? What the smaller than usual poops indicate is a gut slowdown, and with rabbits this can be a dangerous thing as it can then lead to a blockage, which at times can be fatal. I've had two rabbits that have had GI stasis. One unfortunately, died from it, and the other came through it after two weeks of hand feeding and meds. So, it is something to be concerned about, and something you will want to try and correct so that it doesn't get any worse.
You first need to try and figure out what could be the possible cause. The most common has to do with excess sugars and carbs in a rabbits diet. Every rabbit is going to be different. Some rabbits can have treats and never present any digestive trouble. Others are very sensitive and can have very limited, to no treats. My rabbit that came through the stasis, gets zero treats. He can't even have pellets as that will cause him to go into stasis again. He gets hay and some leafy veggies. So for a rabbit with a sensitive digestion, you will either need to eliminate or limit treats, and sometimes the pellets as well. Some other causes of stasis are specific veggies causing gas and discomfort, ingested foreign matter(ex. carpet fibers, cat litter), health problems, sudden changes of food, molting and ingesting hair, not getting adequate hay and fiber in the diet, environmental stressors, or changes in the rabbits life causing it stress. So you will want to pay attention to when your rabbit starts having the small poops and try and pinpoint what may have happened just previous to the gut slowdown to cause it. Did he just have a treat, does it always happen right after he eats his pellets, is he molting, did you just rearrange his cage, did he get spooked by something, did you just have visitors and he was nervous, did you just take him somewhere, did he just rip up a piece of carpet, etc? I realized with my rabbit, that everytime after I just fed pellets, he would either sit in the corner squinting his eyes, or he would lay down with his butt pressed into the air and his belly pressed to the floor, because his stomach was bothering him. So I knew it was the pellets causing the problem. Since I stopped the pellets, he hasn't had anymore stasis episodes.
Water is really important also, in helping to keep a blockage from occurring. If your rabbit drinks from a bottle, then try a water dish, as rabbits generally drink better from a dish. If you can get him to eat more leafy greens like green leaf lettuce or cilantro, that will help. Always introduce new foods in small amounts and one at a time, so you can see if it causes digestive problems, and also to give the digestion time to adjust to the new food. Avoid the veggies that are prone to causing gas. Kale can sometimes be one of those veggies, so try and see if he starts having any of his digestive problems after feeding the kale. What kind of pellets do you feed? Do they have treat pieces mixed in them? You also may want to consider reducing pellet amounts to see if that helps. It will also get him eating more hay, which helps prevent gut slowdowns. And also cut or eliminate treats to see if those may be causing the problem. I know they love their treats, but if you ever have to deal with a rabbit in stasis, you realize it's not worth the risk for rabbits with sensitive digestions. If you find that the gut slowdown isn't food related, then treats can be brought back, but no need to take the risk until you are sure.
This article explains GI stasis really well, and was very helpful to me when my rabbit was first having problems with stasis.