My question involves labor and employment law for the state of: Michigan

So, I have a bit of a story here, and I'm hoping I can find a was to resolve my problem. I was recently "terminated" from my job of 8 years. I believe it is bogus, and maybe illegal?

Here is what happened: One day while working on the job (retail) I had injured my shoulder lifting a heavy item above my head. I didn't realize immediately that I was injured, just that I felt some pain which eased after some time. Eventually as time went on, the pain returned, with increasing intensity. 1 week later, the pain was unbearable, so I approached my manager about the injury. We'll call him "Jack".
(A quick side-note about this manager: Jack is quick tempered and foul-mouthed. He is extremely disrespectful to employees, often degrading them for asking questions, or not being able to complete difficult goals "quickly enough". This is not my opinion of his behavior solely, as all employees under his management have commented on his bad behavior. He has been my manager for the last 8 months. This is information isn't for a legal check, but to help illustrate how the following happened.)
After 3 days of being denied to file an injury report, due to lack of time he claims, I finally notified the Secondary Store director of the situation, and later that night Jack took my injury report down. He also apologized that night for being "mean and snappish". The next day, his attitude was worse then ever! After an incident when I informed him we had a problem in the backroom, he sarcastically replied, "Thanks for that! Yeah, all the machines are f***ing down right now. But really, thanks! Thanks for telling me! I didn't know that already!" This continued with no verbal response from me, at which point I turned away to walk back to my task. He yelled after me, "I'm just being a butthead to you dude! You know I'm kidding, right?"

As I approached my work area, he stepped out to where I was, and began slapping my injured shoulder, saying, "You know I'm just messing with you, right dude?"
I yelped out that he was "slapping my hurt shoulder", and , "Stop!". He didn't stop immediately, but when he did, he simply walked away without word. Needless to say, the shoulder was now numb and my arm ached, my fingers tingling. Pain was shooting from my neck down to my lower-side.
I immediately went to the Secondary store director and told her what had happened, and that I needed to go to the Med-Clinic immediately.
After filing a second injury report concerning this incident, I went to the clinic. The result was: My Trapezius muscle was severly aggravated and the shoulder ligaments were inflamed.
Later that day I filed a verbal abuse and assault grievence with my Union.

OK, so thats the long part of the story. Here is where I need some legal advice:

I was told by many people after I filed with my Union that the Primary store director was a dirty player, and she would find any little reason to try and fire me, because she didn't want to deal with Worker's Comp issues, and most importantly, "Jack" assaulting someone. Apparently Jack was promoted by her in a previous store. She had only taken charge of my store less then 1 month ago. My own Union rep warned me that since "Jack and her are so buddy-buddy, we may have trouble."
Sure enough, the next day she calls me into her office, and tries to "direct deal" with me, which I am told is illegal in Michigan when a grievence is filed through a Union. The offers were: "I'll talk to him, if you let this go." and " If you are'nt comfortable working with Jack, I can help you transfer."
I politely declined, and informed her I was working this through the Union.

I was then called into the Store Director's office 2 weeks after my injury report was made. She said I had destroyed company property and created a hostile workplace. This was due to the fact that I had written on a price Gun. What was written was a fellow employee's name, which maybe mistaken as a homosexual slang word.
2 things concerning this: 1) I was told by both Jack and another manager that we are supposed to write our names on our guns so that they won't be stolen as easily, so I'm not sure how I destroyed anything, especially since the gun still operates, and the name can be removed. 2) If approached by a perverted mind, the name could seem offensive, I'm not splitting hairs. It was his last name, period. No alteration was done with his name.

So, now I am terminated. Do I have any legal recourse? This is an extremely flimsy excuse for termination, and I personally feel it was done because I was injured, and one of her managers are tied to my injury.

Although opinions are respected, I've heard plenty. I need some solid facts on what my next course of action should be, or if there even is any further action I can take.

Thanks for reading!