The reigning MVP left Game 2 of the WNBA Finals just a few minutes into the first quarter due to back spasms. A further update on her status will be provided by the team on Saturday.
Delle Donne was also limited by back issues during the 2014 championship series.
The Connecticut Sun capitalized on her absence to knot the series at 1-1.
Delle Donne scored 22 points in the Mystics' Game 1 victory and is averaging 17.8 points per contest during the postseason.
The six-time WNBA All-Star was second in scoring (19.5), fourth in 3-point percentage (43%), and fifth in rebounding (8.3) during the regular season.