Alabama Workers' Compensation Dispute. Do We Have Grounds To Sue His Employer For Compensation?

I'm looking for legal advice regarding my husband's situation with his employer in Alabama. We are trying to understand his legal rights and whether we have grounds to pursue financial compensation or a lawsuit against the company.
My husband injured his arm approximately 10 years ago while serving in the United States Navy. He underwent surgery to repair the injury, which included a suture being placed in his arm. He recovered, was medically cleared, and was released to return to work without restrictions. For the past 10 years, he has been able to perform his normal job duties without any problems related to that injury.
Recently, while working, he was lifting a windshield when he injured that same arm. We believe this incident may have caused the original surgical suture from his military injury to fail. He ultimately needed another surgery to repair the damage. The surgery he recently underwent through the Department of Veterans Affairs was different from the surgery he originally received in the Navy.
He initially went to urgent care, where the doctor evaluated his injury. The doctor told us that if workers' compensation refused to cover the injury, she would document her medical findings in a way that could support a potential lawsuit in our favor.
He eventually had to seek treatment through the VA to get his arm repaired rather than receiving treatment through workers' compensation. He has since undergone surgery and is currently on short-term disability.
There is another concerning issue. Last year, before this workplace injury ever happened, his employer made him sign a document stating that if he sued the company, he would be terminated. This was before any of the current circumstances occurred.
We are concerned that his employer is using his military-related injury from 10 years ago as a reason not to take responsibility for an injury that happened while he was performing his job duties, despite the fact that he had recovered and been cleared to work without restrictions.
We have looked into Alabama Code § 25-5-58 regarding preexisting conditions, § 25-5-77 regarding medical benefits, and § 25-5-11.1 regarding retaliatory discharge.
We are specifically trying to determine:
Can workers' compensation legally deny his claim simply because he previously injured the same arm 10 years ago, despite being fully recovered and cleared for unrestricted work?

Would this qualify as an aggravation of a preexisting condition under Alabama law?

If the workplace incident caused the previous surgical repair to fail and required another surgery, would that constitute a compensable workplace injury?

Is the employer responsible for medical expenses and lost wages resulting from this incident?

Is the document threatening termination if he sues the company legally enforceable?

Do we potentially have grounds for a separate lawsuit against the employer, particularly regarding the document he was forced to sign or the way they have handled this injury?

What types of financial compensation could he potentially pursue beyond having his medical treatment covered?

We are not just looking to have his medical bills paid. We want to know whether there are grounds to hold the company accountable financially for what has happened and whether he may be entitled to additional compensation for lost income, damages, or other losses.
Has anyone dealt with a similar situation in Alabama? We would really appreciate advice from Alabama workers' compensation attorneys or anyone familiar with employment litigation. We are also interested in recommendations for attorneys who handle denied workers' compensation claims and potential employer retaliation cases.

Location: Alsbama