talkSPORT pundit and Bleacher Report columnist has commented on the latest Manchester United transfer news and views Borussia Dortmund man as a must-buy.
With Manchester United's two major summer purchases - Luke Shaw and Ander Herrera - having been completed prior to the official start of Louis van Gaal's tenure as full-time manager, the Dutch maestro is yet to make his first signing.
In pre-season, Manchester United have experimented - successfully - with a 3-5-2 formation, however, Collymore does not feel that the centre back trident of Chris Smalling, Jonny Evans and Phil Jones is strong enough at the elite-level.
He said: "The one issue United had last season was that they conceded far too many goals, even though they had the best away record in the Premier League. They conceded at home and far too frequently.
"With Louis van Gaal playing three central defenders in Smalling, Evans and Jones… I don't think any of them, with the greatest respect, are of the world class standard that is expected at United.
"Mats Hummels would add that, as well as adding that vital experience - he's a World Cup winner. He would fit in well in a defensive three at United."
In the recent World Cup tournament in Brazil, the 25-year-old played six times and made 16 tackles, 29 clearances and 11 interceptions whilst also returning an 88% passing accuracy from 289 pass attempts.
Hummels has three years remaining on his BvB contract but is reportedly available for £20 million.