Over 40 percent of the world's professional footballers have experienced delayed payment of wages, according to a wide-ranging survey published by global players' union FIFPro yesterday.In the survey, carried out by the University of Manchester, 41 percent of the 13,876 players who responded had been forced to wait for their salaries over the past two seasons."It's a wake-up call for clubs and governing bodies," FIFPro General-Secretary Theo van Seggelen told reporters during a recent briefing in London. "We cannot accept it any longer." The FIFPro Global Employment Report 2016 also found 9 percent of players had suffered from violence and 7 percent had been approached to fix matches.FIFPro hopes the survey, which is the biggest of its kind, will shed light on the problems faced by players playing outside glamorous championships such as England's Premier League or Spain's La Liga. The median net monthly income of players surveyed was $1,000 to $2,000, with 60 percent of respondents earning under $2,000 per month. FIFPro has used the example of Nigeria international Michael Uchebo, who has not been paid by Portuguese top-flight club Boavista since April, to illustrate its findings on late payments.The 26-year-old striker has been prevented from playing since the end of last season and, according to FIFPro, risks eviction from his house. He has been banned from first-team training and has posted footage on social media that appears to show him being forcibly removed from Boavista's gymnasium and threated with violence by security staff."I don't understand why Boavista treat me like this," Uchebo said during a press conference in Lisbon organized by the Portuguese players' union."I asked them if I did something wrong. They are treating me like a slave."World governing body FIFA's rules on overdue payments allow clubs to be 90 days late and the survey found 78 percent of players experiencing salary delays were paid within that timescale. FIFPro wants the non-payment buffer to be reduced to 30 days, in the short term, and ultimately abolished.