Van Dijk is on the books of Southampton at the moment and is one of the best central defenders in the Premier League.
Wanyama, who operates as a defensive midfielder, is a key figure in the current Tottenham Hotspur team.
The 26-year-old Kenya international was on the books of Celtic from 2011 until 2013 when he joined Southampton for a transfer fee reported by BBC Sport to be worth £12.5 million.
After three impressive seasons at the Saints, the former Beerschot midfielder moved to Tottenham in the summer of 2016.
Van Dijk joined Celtic from Dutch club Groningen in the summer of 2013 and played for the Glasgow giants for two seasons.
Southampton paid the Hoops a transfer fee of £13m, as reported by BBC Sport, in the summer of 2015 in order to secure the services of the 26-year-old Netherlands international centre-back.
Stoke midfielder Fletcher, who has also played for Manchester United and West Bromwich Albion, has said that both Van Dijk and Wanyama are superstars in the Premier League.
“You only have to look at Virgil van Dijk and Victor Wanyama for examples of players who have been turning it on at Celtic and who have become superstars in England,” Fletcher told The Glasgow Evening Times.
“They are a good team with good players – you can be pretty certain about that. There are a number of players who could walk out of Celtic and into an English team and not just play but excel. I’d have no doubt about that.”