The England international, who is United's top goal-scorer this season with 29 goals across all competitions, missed their 2-0 win over Wolverhampton Wanderers last week due to a leg injury.
United are fourth in the standings with 66 points, one more than fifth-placed Liverpool, who have played a game more.
"Rashy trained well the whole week but today he reported he is ill. We have to see how he recovers during the day and see tomorrow," Ten Hag told reporters ahead of Saturday's trip to Bournemouth.
The Dutchman also added that midfielder Scott McTominay (26), who has missed United's last nine matches due to an injury, has returned to training and will be in contention if he is fine today.
Ten Hag's praised Gary O'Neil's Bournemouth, who have moved out of the relegation zone, winning four of their last seven league games. Bournemouth are 14th with 39 points, with two games to go.
"They are in the Premier League and three games before the end of the season they are definitely in the Premier League next season as well. It's massive. You can see clear patterns, so well done," Ten Hag said.
Following Manchester United's clash against Bournemouth with Flashscore.
