Defending men's champion Novak Djokovic begins his quest for a seventh title against South Korea's Kwon Soon-woo, ranked 75th in the world.
The early focus at the All England Club will be on 23-time Grand Slam singles champion Williams, who has dropped to 1,204th in the world rankings and is unseeded for the tournament, which starts on Monday.
The 40-year-old, who took part in the doubles tournament in Eastbourne this week, has not played singles since she suffered an injury during her first-round match at Wimbledon 12 months ago
Tan, 24, is ranked 113rd in the world.
Top seed Iga Swiatek, who won the French Open earlier this month, opens her campaign against Croatian qualifier Jana Fett.
Poland's Swiatek, 21, has won 35 consecutive matches leading into Wimbledon.
Williams's preparations for Wimbledon suffered a blow after her doubles partner Ons Jabeur withdrew from the Eastbourne tournament because of a knee injury on Thursday.
The American won the last of her seven Wimbledon singles titles in 2016 but reached the final in 2018 and 2019 after returning from having a baby.
Wimbledon is widely considered Williams's best chance of claiming a 24th Grand Slam singles crown to equal Margaret Court's all-time record.
The last of the her Grand Slam singles titles came at the Australian Open in 2017.
Speaking after Wednesday's doubles match, Williams had said: "I feel good. As good as one can feel after having such a long time off."
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