According to ESPN FC's Mark Ogden, the three did not travel to London with their team-mates:
Mark Ogden @MarkOgden_
Rooney, Rashford and Martial all out of #mufc trip to Chelsea. Bad timing, but perhaps convenient excuse for Mourinho if United lose..2017-3-12 19:49:10
BBC Sport reports Martial and Rooney are out due to injury, while Rashford is ill.
One of the three was expected to replace the suspended Zlatan Ibrahimovic at the striker position. Instead, manager Jose Mourinho could opt for a major tactical switch and start with a false nine.
HLN's Kristof Terreur suggested another solution, with midfielder Marouane Fellaini moving into attack:
Kristof Terreur 📰 @HLNinEngeland
No Rooney, no Rashford, no Martial on the #MUFC train. Zlatan suspended. A false '9' or Fellaini upfront? #mufc #cfc https://t.co/PzyOJH5qYX2017-3-12 17:35:05
Mourinho will have his second shot at beating former club Chelsea at Stamford Bridge, and he'll be extra motivated following the 4-0 defeat earlier this season.
The Red Devils have struggled for form of late and could use a boost of momentum after the draw in the UEFA Europa League against Rostov. Chelsea are cruising to the Premier League title and enter Monday's clash rested and without major absentees.
The Blues' defensive stability has been their biggest strength this season, and facing Conte's troops without a natural striker would be a nightmare scenario for United. Mourinho's men struggle finishing chances as it is, per WhoScored.com:
Do Manchester United have what it takes to keep pace with their top four rivals without Zlatan Ibrahimovic? https://t.co/T0qrHnVapp https://t.co/askKqJsWsF2017-3-11 19:00:03
Per BBC Sport, Ibrahimovic's three-match suspension for a violent incident involving Bournemouth's Tyrone Mings will start against Chelsea.