I want to know if I can build a warrior or small size soccer robot with LEGO parts? If not, are there any better options?
An option that comes to mind is building a Raspberry Pi-based robot. But it's not likely to be small nor easy to put together, code and all.
I think going for a LEGO robot would be easiest; motors, electronics and power source have all been taken care of. You "only" need to connect them and program the EV3 brick. There are numerous YouTube videos of Mindstorms soccer robots that can inspire you.
It's easy to use Lego Mindstorms EV3 to build small robots. There are competitions such as the WRO where EV3 soccer bots compete. Sensors like IR seekers from HiTechnic are used to detect the "football" which is an IR emitting ball. As for a warrior, it is hard to balance Lego robots to make something which can walk but you could make the warrior run on wheels or slightly complex quad-walker mechanisms.