Mohamed Lahyani (born 27 June 1966 in Morocco) is a Swedish tennis umpire. He is a Gold Badge Chair Umpire certified by the Association of Tennis Professionals. He is noted for presiding over the longest match in professional tennis history at the 2010 Wimbledon Championships, the Isner–Mahut match at the 2010 Wimbledon Championships that lasted 11 hours 5 minutes (Isner won).
Lahyani later said he was so gripped by “an amazing match” that he couldn’t even think of “eating or needing a bathroom. After the match, he was presented with a crystal bowl, a Wimbledon tie and silver cufflinks.
At the 2018 US Open, Lahyani made headlines after his controversial behavior during the match between Nick Kyrgios and Pierre-Hugues Herbert, when he climbed down from his chair and encouraged Kyrgios to put in extra effort. At the time Kyrgios was losing by a set and a break, but after Lahyani’s comments, recovered and won the match. After criticism from current and former players, Lahyani was suspended for the next two tournaments.