Luke Shaw and Fred could miss Manchester United's Premier League fixture at Chelsea on Sunday.
Shaw did not travel to Villarreal for United's penultimate Champions League group stage game on Tuesday night, having suffered concussion for the second match running at Watford last Saturday.
Fred twisted his ankle in the first-half of United's 2-0 win at Villarreal but still played 90 minutes and had a key role in both of their goals in the 2-0 win.
Edinson Cavani has been absent for the last two matches with a tendon injury while Paul Pogba (thigh) and Raphael Varane (hamstring) are both out.
Michael Carrick said: "We've got two or three different little issues that we're waiting to see how the boys come through. It's never ideal, you want a full squad to pick from but there are one or two we're waiting on.
"Luke took a bang on the head and was concussed three weeks ago and he took a bang against Watford. We assessed him during the week and will make a call on how he is.
"Fred twisted his ankle the other night, he managed to carry on, which was pretty incredible, to be honest, seeing the game out and playing a big part in winning the game for us. We'll have to see how that settles down.
"There are one or two others as well. But we'll be strong tomorrow travelling down."
League leaders Chelsea are 12 points clear of United and the appointment of coach Thomas Tuchel in January has proven to be transformative. Chelsea won their second Champions League title in May and have lost just once in the league so far this term, conceding just four goals.
Carrick added: "You've got to be hugely impressed by the way they go about things, Watched quite a bit of them and super intense, well organised, really good movement across our backline and their frontline, and very good at connecting with the midfield, with the back three building up and connecting into midfield, narrowing up and giving you problems with the wing-backs.
"Really aggressive and playing really high, they test your backline and stretch you across the pitch. They've got a really good balance at the moment, confidence is high, they've had some really terrific results. They're on a high.
"I'm well aware of the challenges that we face but I'm looking forward to it because it is a big test and a big challenge but we believe we can go there and get a result there, no doubt."
