Jose Mourinho has revealed that he "does not know" if the injury suffered by Ander Herrera in Manchester United's friendly win over Real Madrid will be enough to keep him on the sidelines.

The Spanish midfielder lasted just a few minutes after being brought on at the interval following a collision close to the touchline, leaving him clutching his ribs as he made way at the Levi's Stadium.

Mourinho says that Herrera was in a lot of pain but is unsure exactly of the severity of the damage, which may keep him out of the remaining United States tour game against Barcelona in the early hours of Thursday morning.

"It must at least be very painful because for Ander to come off, it has to be very painful," he told reporters. "I want to wait and see what it is.

"I always say to the players that you don't risk anything in friendly matches. If you feel something is coming, even if it is a little injury, get off because the result is not important. It was very painful, it was in front of the bench, it was a bad contact. Maybe it is his ribs but I don't know."

United went on to win the game 2-1 on penalties following a 1-1 draw in normal time, with Jesse Lingard and Casemiro registering inside the 90 minutes.