The midfielder succeeds Max Kilman, after his departure for West Ham United.
O'Neil stated, “He was a standout choice for me. We have some real good leaders in the group, and I’ll definitely lean on all of them throughout the season, but I think Mario with where he is, it’s really good timing for him. He has big respect from the players, around all the different groups, and manages to get on well with loads of them and drives standards.
“As a player, you go through spells in your career of being young and full of potential, to being an established starter, and then you go into the leadership category. I feel Mario was in that already and this confirms it for him and gives him a real drive and focus on what he needs to be for the group now.
“We had a little chat to check his thinking and he was really pleased and excited, and he’s done it really well since he’s taken over the last few weeks. He’s been excellent. I thought it would help him make the next step from established player to leader, and the early signs have been really positive – he’s been excellent so far.”
The manager also revealed: “Mario knew about it fairly early. With the players coming back at different times, making an announcement was tricky. I’d have liked to wait until we were all together as a group, but it’s not always possible to do them in the perfect way. Nelson, Joao, Sa and Pedro are not back yet, but Mario’s known about it, and he’s been putting things in place that he thinks are important for him and the group.
“He’s very good at portraying the messages that we want and what the group likes. I’m excited to see what we can do, what Mario can do, and how the group can perform this year with Mario as their captain.”