Virgil van Dijk hit out at his treatment from Southampton as he made public his intention to leave St Mary's.The 26-year-old said he felt "insulted" by suggestions he had refused to train and has grown frustrated at the Saints turning down approaches from "multiple top clubs" this summer.The Holland defender, who joined the club from Celtic in 2015 and is a long-term target for Liverpool, revealed he had handed in a transfer request.Van Dijk was left out of the Saints' pre-season training camp in France last month, with manager Mauricio Pellegrino saying "psychologically he is not 100 per cent", while Southampton have insisted he is not for sale. In a statement released by his management company, Van Dijk said he had not refused to train at any time and that his desire to leave owes to his ambition to challenge for trophies. "It is with regret that I can confirm that I have handed in a transfer request to leave Southampton Football Club," Van Dijk said. "I feel I have no alternative after I was given notice of the club's intention to impose a disciplinary sanction against me of a fine equivalent to two weeks' wages. I will be appealing what I feel to be an unjustified sanction and their inability to follow the correct disciplinary protocol in due course."Over the past six months I have held numerous discussions with representatives of the board, the former manager Claude Puel as well as the new manager Mauricio Pellegrino to inform them all of my desire to leave in search of a new challenge."I am incredibly ambitious and want to achieve as much as I possibly can to fulfil my potential in what is a very short career as a professional footballer. I want to play European football again and challenge for major honours and as such I would like Southampton to consider the interest in me from top clubs should it still exist."I have been left frustrated by the club's position that I am not for sale and am disappointed that enquiries from multiple top clubs have been consistently rebuffed."The period of time that I have just spent injured and unable to play has put a number of things into perspective and made me realise just how important it is to take major opportunities should they arise."I have consistently relayed my feelings to senior management at Southampton in what I believed to be private and personal conversations. Disappointingly, these conversations have regularly found their way into the media."I would also like to make clear that I have never once refused to train."As a proud professional I am insulted by the suggestion that it was me who refused to train and so feel it is important to point out the true version of events."I had very much hoped to retain the good relationship I've always enjoyed with everyone at the club, especially the fans, but in light of everything that's happened this has now been seriously affected."I have nothing but gratitude to everyone at Southampton for giving me the opportunity to play in the Premier League."However, the time for me to move on is now and I hope to be able to work with the club to find the best resolution to suit all parties."