Louis van Gaal revealed David De Gea missed Manchester United's 1-0 win over Club America with a minor injury.
De Gea, 24, is a target for Real Madrid but United have held out for a world-record transfer fee for a goalkeeper, and are reportedly willing to keep the Spaniard for the last year of his contract even though they risk losing him on a free transfer.
Morgan Schneiderlin scored the only goal on his debut for a United side who were also without Antonio Valencia, who had undergone ankle surgery in the summer and did not make his comeback.
The United manager said that De Gea is not a doubt for the start of the Premier League season.
"David De Gea and Antonio Valencia were injured, minor injuries, but we cannot take any risks," said Van Gaal in his news conference in Seattle.
Van Gaal opted not to use Marouane Fellaini, who was sent off on the final day of last season against Hull, and explained: "Marouane Fellaini is suspended for the first three [Premier League] matches so he has a longer time to prepare himself and I need to see other players."
United have made four summer signings and Memphis Depay, Matteo Darmian, Bastian Schweinsteiger and Schneiderlin all featured, with the former Southampton man heading in Juan Mata's cross after five minutes.
Van Gaal was delighted to see the midfielder find the net, explaining: "He scored with Southampton, I believe five goals, so it is not a coincidence but we have practised this with him so I was very pleased with the performance."
The United manager suggested that Daley Blind, who spent much of his first season at Old Trafford operating either at left-back or in midfield, could be deployed in the centre of defence.
"It could be," he said. "Marcos Rojo is not here. He shall also come on July 25. I want to play always with a left-footed central defender and Blind can do the job.
"Maybe he shall play there but all the players can play there. Last year it was [Phil] Jones and [Chris] Smalling, and even [Paddy] McNair has played there. But my preference is a left-footed defender and with Rojo and Blind we have two."
Sources have told ESPN FC that United are willing to sell Jonny Evans, who has spent much of his career operating as a left-sided centre-back, which could provide an opening for Blind.
Van Gaal does not seem in a rush to buy a new striker, but the coach also hinted he could enter the market for a forward if he deems it necessary.
"I am not worried about depth of forwards. We still have [Wayne] Rooney. He can play in the striker's position," Van Gaal added.
"We also have Chicharito [Javier Hernandez], [James] Wilson and maybe a surprise, you never know. It is a process. I am not worried about that position."
Information from the Press Association was used in this report.