Obviously, his brothers are very important. Donatello would be crucial as he could try to diagnose Leo's illness. Raph would be there to provide protection and strength if any threats come while Leo is vulnerable. Mikey would be the emotional support, trying to keep Leo's spirits up.
Maybe it's a new villain in the fanfiction. Some powerful and evil character who sees Leo as a threat to their plans. This villain could use their unique powers or weapons to harm Leo. For example, a villain with the ability to control electricity could zap Leo and cause internal injuries.
Raph usually gets really angry. He blames himself for not being there to protect Leo or he gets mad at the enemy who hurt Leo. He'll be the first to want revenge and will be very protective of Leo while he's injured.
In the 'tmnt leo gets injured fanfiction', one possible scenario could be that Leo gets injured during a fight with the Foot Clan. Maybe he underestimates their new weaponry and gets a deep cut on his arm. Another could be that he's injured while trying to protect his brothers from a falling building, getting his leg trapped under rubble.
One common theme could be the shock and confusion among the other turtles. They would have to deal with a situation that is completely out of the ordinary for their world.
One common scenario could be during a battle with a powerful enemy. For example, the Foot Clan might set up a complex trap and Leo, being the leader, might rush in to protect his brothers and get seriously injured. Another could be in a training accident. Maybe he's trying a new and difficult move and it goes wrong, resulting in an injury.
One common plotline could be the other turtles trying to take care of Leo. They might struggle to figure out what's wrong with him at first. For example, Donatello would use his scientific knowledge to run tests. Another plotline could involve Leo being stubborn about accepting help while he's sick, thinking he can still lead and protect the team even in his weakened state.
One common way is in a fight with a powerful enemy. Maybe a new mutant or a really tough Foot Clan member. Another way could be through some sort of accident, like a trap that was set for the turtles.
Leo would likely take charge. He'd be calm on the outside but worried inside. He'd make sure Donnie gets proper rest and tries to organize the others to help. Raph might be a bit gruff at first, but he'd actually be really concerned. He might offer to get supplies or guard Donnie while he sleeps. Mikey would be the most emotional. He'd probably be constantly by Donnie's side, trying to tell him jokes to make him feel better.
In the traditional TMNT universe, male turtles like Leo getting pregnant goes against the biological norms of the franchise. However, in fanfiction, anything can be reimagined. Some fanfiction might use magic or some out - of - the - box concepts to make such a situation possible, but it's not part of the official TMNT lore.