Manchester United boss Ole Gunnar Solskjaer has explained the decision to give the armband to David De Gea.
The Spanish goalkeeper was leading out United against Wolves in their second Premier League game of the season.
Solskjaer believes that De Gea is one of the team's leaders in the dressing room, even though he has not committed to a new contract yet.
The Norwegian said to United's official website about the captaincy: "David's wearing the armband because at the moment he is very much a leader in that group and he knows that we value him as one."
United's club captain is Ashley Young, but he was only on the bench for the game. It would make De Gea their de-facto vice captain.