The Belgian and English youngsters have shone in the Red Devils' pre-season fixtures with the pair both scoring in David Moyes' side's 5-2 win over Kitchee SC on Monday.
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"They have taken their chance,” he told the club's official website.
"It’s good that the manager has given these young players a chance and they have really taken their chances.
"I think all of them have made a claim for the start of the season and they are all in with a good shout."
Januzaj, who has impressed on United's pre-season tour of Asia and capped his fine displays with a goal in Hong Kong, is pleased with his performances but is aiming to continue to improve.
"I have done some good stuff [during the tour] and I hope to keep going," the Belgian added.
"That is what I am going to do. I am going to work hard and try to keep doing what I am doing."
United have one more friendly on their tour before heading back to England, which will see them face AIK in Stockholm on August 6.