Martinez says he was taken aback when he learned of Oâ€™Neillâ€™s departure â€“ but reckons things like this go with the territory of being in the Premier League.
â€śObviously we donâ€™t know what the internal situation is at the football club,â€ť Martinez told the Wigan Evening Post.
â€śI have to say it has come as a surprise to everyone that Martin left before the end of the season. But changes are normal these days â€“ you just learn to get on with it.
â€śThe new man will bring in a completely different approach, and probably that is part of the reason why this league is the best in the world.
â€śItâ€™s colourful, itâ€™s exciting, itâ€™s unpredictable. Thatâ€™s why people love it so much.
â€śIâ€™m sure the media will be happy, but Sunderland are a phenomenal club with a great tradition and theyâ€™re capable of finishing the season strongly.â€ť