Manchester United have arguably the richest history in the Premier League but it has taken countless signings to put them at the top of the food chain. Sir Alex Ferguson always had a keen eye for transfers.However, there were also times when he failed to identify the right prospects. Ferguson would often scout exciting talents by himself while the four managers that have followed him normally delegated that duty to the scouts.Manchester United have never shied away from dipping into the market in JanuaryThe 13-time Premier League champions have often dipped into the January transfer market. Players like Patrice Evra, Nemanja Vidic, Andy Cole, and Bruno Fernandes are evidence of that. There are also some players who have proved that January is not the best time of the year to invest in new talent.On that note, let us take a look at the 5 worst January signings in Manchester United history.Note: Players that were signed on loan were not considered for this list. #5 Diego Forlan (2002-2004)Blackburn Rovers v Manchester UnitedDiego Forlan is perhaps one of the few players to become a superstar after leaving Manchester United. The Uruguayan international signed for the Red Devils in January 2002, as they swooped in for him away from Middlesbrough in the 13th hour. Sir Alex Ferguson was looking for a backup to Ruud van Nistelrooy and he believed the Independiente ace would do the trick.The Athletic UK@TheAthleticUK"I had to leave Manchester United. Something inside told me I needed to start again..."With #MUFC and Villarreal set to do battle in the Europa League final, Diego Forlan discusses his 2004 move between the two with @AndyMitten.2:01 AM · May 22, 202124113"I had to leave Manchester United. Something inside told me I needed to start again..."With #MUFC and Villarreal set to do battle in the Europa League final, Diego Forlan discusses his 2004 move between the two with 📝 @AndyMitten.Despite making 18 appearances across all competitions in the 2001-02 season, the South American failed to score a goal. Forlan got off the mark the following campaign and also scored important goals against Chelsea in the Premier League and the EFL Cup. He played his part in winning the 2002-03 league title, but could never turn into a talisman for the Red Devils.Forlan had a quiet 2003-04 season, following which he was sold in the summer. He later went on to make a name at Atletico Madrid while also starring for his national team at the 2010 World Cup.Manchester United fans still have fond memories of him. However, the hierarchy at the club will regret that a player of his potential could never transform into a world-beater at Old Trafford.#4 Dong Fangzhou (2004-2008)Beijing Hyundai v Manchester UnitedDong Fangzhuo was often the forgotten star at United during their period of success in the 2000s. The China international arrived at Old Trafford in January 2004 and became the first-ever East Asian player to be signed by a Premier League club.Pro:Direct Soccer@ProD_SoccerSome good suggestions so far. Ever remember Dong Fangzhuo? Nope nor do we. 3 appearances in 4 years at @ManUtd... http://t.co/Dzs9749FcB4:24 AM · Jan 31, 2014823Some good suggestions so far. Ever remember Dong Fangzhuo? Nope nor do we. 3 appearances in 4 years at @ManUtd... http://t.co/Dzs9749FcBHowever, Fangzhou was not allowed to play for the club due to difficulties in landing a work permit. As a result, he joined Belgian side Royal Antwerp on a loan deal. Fangzhou enjoyed success in his two-and-a-half-year stint in Belgium as he scored 30 goals in 53 appearances for the Belgian Pro League outfit.The Chinese international was recalled by Sir Alex Ferguson for the 2007-08 season but he only managed to make one Premier League appearance for his parent club.Fangzhou could not adjust to the pace or the intensity of the league and mutually terminated his contract with the club in 2008. Fangzhuo retired in 2014 but not many remember his time in the famous red jersey.