The first sentence looks good, You can also use "lag behind" in a physical sense, for example: "John lagged behind the others in the race because he had crutches"  or  "Steven's reading skills were lagging behind the others since he didn't practice at home."

Your second sentence above is not quite right.  If you're talking about someone who is on the team, but wasn't there because he was sick, and you're trying to communicate that YOU missed him, you would say:  "I missed him because he was sick".  

You usually use the phrase "missed out" when something fun, important and or exciting happened, and someone who would normally have been there wasn't there.  It's a way to communicate that they weren't a part of the excitement that they would have experienced under normal circumstances.  Here is an example:  "Our boss brought cupcakes to work, but Jenn missed out because she was sick at home"   or it could show that they missed an opportunity:  "John saw he had chosen the winning lottery numbers 2 weeks after his ticket expired.  He was so angry to have missed out on his prize."

Hope that helps!