According to Alyson Footer on twitter:
“Regarding your questions about why Lyon’s shoulder weakness issue wasn’t addressed earlier:he was getting daily treatments for tendinitis, but he felt that he was strong enough to pitch through it, and there was nothing showing up to trainers that suggested he was badly hurt. It was a situation where they were monitoring the shoulder, but Lyon felt pretty good through the process. Obviously, as time went on the shoulder grew weaker. So now he’s being examined and we’ll know more after the MRI.”
The short: Melancon has been moved to the closer spot while Lyon recovers from his ailing shoulder. It could be a long run thing since tendinitis is a tough injury with which to deal. We wish Brandon the best, and wish him a speedy recovery so that he can return to the bullpen. Though, a pitcher like him is not ideal for the closer role, he could be a real innings eater in the set up role.