The midfielder is yet to win his first cap for his country, but could make his debut for Steve Clarke’s side after a good start to the Premier League campaign for the Blades.
Fleck recovered from a hamstring injury picked up in the second game of the season against Crystal Palace and has regained his place in the side, putting in a man-of-the-match display against European champions Liverpool last week.
The midfielder is expected to once again line up in United’s midfield this weekend when they travel to Vicarage Road to face Watford, and Wilder said: “John has come back very strongly. We still feel he can do even better and score in that final third.
“As a young boy at Rangers he played as a centre forward and hopefully the confidence and belief that regular Premier League and international football will give him will make him even better.
“He thoroughly deserves it as he’s been incredible. We brought him in on a free transfer from Coventry when we were in League One and he’s embraced every level since and moved forward.
“He got injured, which was disappointing for him and us, but got back in the team and has kicked on.
“Being called up again is a great reward for him and hopefully he can do himself justice when he goes up the road.”