Manchester United were "forced" to sign PSV Eindhoven forward Memphis Depay early because of interest from French Ligue 1 leaders Paris St-Germain.
Old Trafford boss Louis van Gaal said the club wanted to wait until the summer to bring in the 21-year-old Dutch winger.
But after announcing a deal in the region of £25-30m, Van Gaal said: "I have been forced to sign him.
"I had to handle it otherwise he would have signed for PSG," he added.
Depay, who has scored 21 goals as PSV won this season's Dutch title, has signed a contract believed to be until 2019, with the option of another year.
He will join in June, subject to a medical.
Tottenham reportedly had a bid for the player turned down last year and Depay had attracted interest from a number of clubs across Europe, with PSG and Liverpool reportedly keen to sign him.
"When you sign a player you disturb the focus of your present group of players," Van Gaal said.
Depay told Manchester United's website: "It was a little difficult with all the speculation about my future, but now I've chosen to sign for Manchester United and my dream came true."
|What will Manchester United get from Depay?|
When asked why the Dutch international would have signed for the reigning French champions PSG instead, Van Gaal replied: "Because at that time he was not reached by me.
"I don't want to speak with players before the season has ended - I have also a feeling to my players. But now, because of the close relationship I have with PSV, I could handle it."
Van Gaal also told Friday's press conference that midfielder Michael Carrick will not play again this season after the England international sustained a calf injury in the 4-2 derby victory over Manchester City last month.