The 1991 German Open was a tennis tournament played on outdoor clay courts and was part of the ATP Super 9 of the 1991 ATP Tour.
 It took place at the Rothenbaum Tennis Center in Hamburg, Germany, from May 6 through May 13, 1991.
 Sergio Casal and Emilio Sánchez won in the final against Cássio Motta and Danie Visser, 7–6, 7–6.
Athletic DNA (ADNA) is an American sports apparel company.
 Founded in Seattle in 2007, ADNA began by training young tennis athletes, which evolved into sponsoring Select Junior Tennis players, and then expanded to manufacturing clothing for youth and adult tennis players.
 ADNA has since spread to professional tennis, and currently sponsors players on the ATP Tour & WTA Tour.
Mark Gurr (born February 18, 1966) is a retired tennis player from Zimbabwe, who represented his native country as a qualifier at the 1988 Summer Olympics in Seoul, South Korea.
 There he lost in the first round of the men's singles competition to Spain's Sergio Casal.
 He lost in the second round of the men's doubles competition to Sweden's eventual bronze medalists Anders Järryd and Stefan Edberg, while partnering Philip Tuckniss.
Natasha Zvereva, or Zverava, (born Natallya Maratawna Zverava; Belarusian: Наталля Маратаўна Зверава; 16 April 1971) is a former tennis player from Belarus.
 Zvereva was the first major athlete in the Soviet Union to demand publicly that she should be able to keep her tournament earnings.
 The team of Zvereva and Gigi Fernández won more women's doubles titles and Grand Slam women's doubles championships than any other team since that of Martina Navratilova and Pam Shriver.
Sergio Casal Martínez (born 8 September 1962) is a former professional tennis player from Spain.
 During his career, he won three Grand Slam doubles titles, as well as the men's doubles Silver Medal at the 1988 Summer Olympics.
The Men's Doubles tournament at the 1988 US Open was held from August 29 to September 11, 1988, on the outdoor hard courts at the USTA National Tennis Center in New York City, United States.
 Sergio Casal and Emilio Sánchez won the title, defeating Rick Leach and Jim Pugh by walkover in the final.
Beatriz "Gigi" Fernández (born February 22, 1964) is a former professional tennis player.
 She turned professional in 1983 and is the first Puerto-Rican-born athlete to win a Gold Medal, and the first to be inducted into the International Tennis Hall of Fame.
Amanda Brown (born 2 May 1965) is a former professional British tennis player who reached the second round of Wimbledon (on two occasions) and the Australian Open, as well as competing for Great Britain at the 1984 Olympics and the 1984 Federation Cup.
 As a junior, she twice won the junior title at the Australian Open, in 1982 and 1983.
 She played her first matches on the WTA tour in November 1982 and her final matches at Wimbledon in 1986.
 During her career, Brown successfully gained victories over players such as Sue Barker, Sara Gomer, Annabel Croft and Gigi Fernández.
The 1990 ATP Tour World Championships was a doubles event held in Gold Coast, Australia between November 19 and November 25, 1990.
 Guy Forget and Jakob Hlasek won the doubles title at the 1990 ATP Tour World Championships tennis tournament, defeating Sergio Casal and Emilio Sánchez in the final 6–4, 7–6, 5–7, 6–4.
"For the Puerto Rican tennis champion born Beatriz Fernández Ferrer, see Gigi Fernández"

Question: Are Gigi Fernández and Sergio Casal both former professional tennis players ?
Answer: yes