Six Washington players have tested positive for COVID-19, and three other players were sidelined after contact tracing determined they might have been exposed to the virus.
Westbrook is listed as questionable for Sunday's game, and he said that he doesn't know if he'll play. Coach Scott Brooks said Westbrook is progressing and looking good so far.
The 7-foot-0 Len has averaged 7.9 points and 6.2 rebounds in 474 games over eight seasons with Phoenix, Atlanta, Sacramento and Toronto. He played seven games for the Raptors this season, averaging 2.3 points and 1.6 rebounds.
The 27-year-old from Ukraine played at Maryland before he was the fifth overall pick by Phoenix in the 2013 draft.
ESPN's Ohm Youngmisuk and The Associated Press contributed to this report.