Olsen's third season began well, but a collision with Chicago Fire goalkeeper Zach Thornton caused an ankle injury that kept Ben out of much of the second half of the season, limiting him to 13 starts and only 1 goal and 3 assists on the year. After he recovered from the ankle injury in late 2000, Olsen was loaned by United to Nottingham Forest of the English First Division, where he immediately impressed and soon became a fan favorite. As a transfer became increasingly likely, Olsen severely fractured his ankle during a December game. During his 18-month absence Olsen required four surgeries and continuous rehabilitation. He finally returned in July 2002 and was able to finish the season with 7 starts and 10 games played.