Erik ten Hag has confirmed the signing of goalkeeper Jack Butland as back-up to first-choice David de Gea.
Butland is set to arrive from Crystal Palace after Newcastle United recalled Martin Dubravka from his season-long loan at Old Trafford.
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When asked about Butland's potential arrival, Ten Hag told a news conference on Thursday: "Martin was recalled and we need three experienced goalkeepers.
"I'm really happy with David. It's quite clear he's our No. 1. He's a really good performer but there's always something that can happen with David as well and you have to be prepared for that so you don't have one."
Sources have told ESPN that United remain in the market for a striker in January following Cristiano Ronaldo's departure.
Joao Felix, Olivier Giroud, Eric Maxim Choupo-Moting, Memphis Depay and Alvaro Morata are among the candidates but, as it stands, Ten Hag is operating with Anthony Martial and Marcus Rashford as his two recognised strikers in his squad.
"We always have to look for that [new signings] as we push the players because good is not good enough," Ten Hag added.
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"We have to push each other and when there are opportunities, the club has to be ready for that. My main focus is to improve the team."
United face Everton at Old Trafford on Friday in the FA Cup third round as they look to end a wait for a trophy which stretches back to 2017 (stream live on ESPN+ at 3 p.m. ET).
Ten Hag's team are still in the Carabao Cup and Europa League and have worked their way into the top four after a run of four straight wins.
"We are in a good position," Ten Hag said. "We are where we want to be but still, we go from game to game.
"We play in many competitions and the focus is from game to game. We don't think too far ahead."