The 28-year-old's career was seemingly in the balance when Red Devils boss Sir Alex Ferguson revealed last month that the Scotland captain was yet to return to training following a long-standing chronic bowel complaint.
But Levein, who named his squad for the upcoming friendly with Australia on Monday morning, confirmed Fletcher is now on his way back to playing competitive football for the first time since November.
Fletcher was restricted to just 10 appearances last term, his last coming against Benfica at Old Trafford in November.
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He turned out just twice in the final weeks of the previous campaign, when the illness first took hold, and last featured for Scotland in a 3-1 defeat to Spain last October.
But when asked if Fletcher could have a role in the national set-up if he had to retire from playing Levein revealed his skipper is on the long road to recovery.
"Darren will be with us at the weekend, he is back in training and he played 45 minutes in a practice match last week," he said. "He is not in the squad because he has not played for Manchester United but he will come back and do a bit of training with us."