Cristiano Ronaldo could join Michael Carrick on the sidelines for Wednesday's match against AaB Aalborg as Manchester United aim to equal a Champions League record and qualify for the last 16 as winners of Group E.
The defending champions will stretch their unbeaten run in the competition to 19 if they avoid defeat against the Danes -- a record currently held by Ajax and Bayern Munich.
Ronaldo is struggling to be fit for the game after injuring his hip in the league victory over Sunderland on Saturday and may not be risked with a busy schedule looming, including FIFA's Club World Cup in Japan.
"Cristiano is doubtful and Michael Carrick is out," manager Alex Ferguson said on United's website on Tuesday.
"Those are the only injury problems we have. Michael should be ready for Saturday [against Tottenham Hotspur], but we'll have to see how Cristiano is."
Veteran midfielder Paul Scholes is expected to be among the substitutes with the experienced Gary Neville starting at right back in place of Brazilian teenager Rafael.
Victory should ensure United top the group unless Spanish side Villarreal, who also have nine points, run riot against already eliminated Celtic.
United have not lost in the Champions League since the semi-final stage against AC Milan in 2007.