Erik ten Hag said Manchester United must wait another 24 hours to discover the extent of the injuries suffered by Leny Yoro and Rasmus Hojlund. (More Football News)
The pair went off injured in the first half of United's 2-1 defeat to Arsenal in Los Angeles on Saturday.
Hojlund opened the scoring in the 10th minute at SoFi Stadium, but Arsenal won thanks to goals from Gabriel Jesus and Gabriel Martinelli.
Yoro, a £52.2million (€62m) signing from Lille, started despite having featured in only half of United's training sessions, and Ten Hag explained his staff were being cautious with the 18-year-old.
"We have to wait, in 24 hours we will hopefully know more, so we were very careful, especially with Leny," Ten Hag told MUTV.
"He did only 50% of the sessions, so it's disappointing he had to come off. But let's be positive and see what comes out."
Ten Hag was pleased with United's display overall. His team mustered only 0.56 expected goals but did have 10 shots to Arsenal's six, while the Dutchman feels Jesus' equaliser should have been called offside.
"A very intense game, a good level," he said.
"We were the better team in the first half, we scored a very good goal – a good move, a good finish. We conceded a goal, but it [should have been given] as offside."
United won a pre-arranged penalty shootout 4-3 at the end, with Andre Onana making two saves and Jadon Sancho converting the winning spot-kick.
Ten Hag added: "It's important – we know all the cup competitions we are in, so penalties can be important.
"Two good saves from Andre. It's important to have a goalkeeper that is good at penalty shootouts and he proved that again. The penalties, except one, were all very good."
Arsenal boss Mikel Arteta, meanwhile, hailed the impact of matchwinner Martinelli.
"One training session and he comes in and plays at that level," he said of the Brazilian.
"That's the mentality of the team and individuals.
"Gabriel looks really sharp. He has changed a lot of things over the summer. You can see. The way he looks, his rhythm, his sharpness.
"You can see it in his eyes. There's some spark there. Now he has a point to prove and that is good."
