can they fire me?!

Okay so I put my 2 weeks into my old job ( I found a new one ) and today I worked but I had to call off because I was sick all morning ( I work in a restaurant and can't risk anything ) but I wanna know if they can fire me for calling off. My manager said if we call off with out a replacement he would fire us. Me being sick was unexpected and random, I just wanna know if they can fire me or not.