"We have to look at Wayne as a No. 10, which is his predominant role," Southgate told the British media.
"In the last two games we've played Dele Alli there and we've played Adam Lallana there. Both are playing very well, scoring and assisting for their clubs.
"Ross Barkley has been playing very well for his club. So there's competition. I can't dress it up any other way."
Alli has scored 13 league goals for Tottenham Hotspur this season, compared with Rooney's two at United.
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"I don't think he (Rooney) expects, if he is not playing every week for his club, to be picked in this sort of situation," Southgate added.
England will play a friendly against Germany in Dortmund on Wednesday before their World Cup qualifier against Lithuania at Wembley on March 26.
(Reporting by Hardik Vyas in Bengaluru; editing by Sudipto Ganguly)
