Owen Hargreaves believes David Moyes needs a box-to-box colossus to make United a force once more.
United are believed to be one of the clubs monitoring Kroos' contract situation with the German champions. The 24-year-old has yet to reach an agreement and should he not commit to a new deal, Bayern only have two more transfer windows in which to sell him, or they end up losing him on a free transfer in 2015.
Moyes could get to see Kroos close up tonight when the Champions League holders continue the defence of their title in the quarter-final first leg tie at Old Trafford.
In the build up to the game both Bayern chairman Karl-Heinz Rummenigge and head coach Pep Guardiola have said they expect the Germany international to remain with the Bavarian giants not only next season, but beyond.
While Hargreaves acknowledges Kroos' undoubted talent, the 33-year-old, who played for both clubs, believes United should instead be looking for an all-rounder like Toure at rivals Manchester City.
"Toni is a brilliant player so he's bound to have options," Hargreaves told the Manchester Evening News.
"He would improve United but he's not necessarily what they only need. They need power, like Yaya Toure gives City. That's what they need so Toni wouldn't be the solution on his own."
"They need to address a few positions, bring a few players in this summer and also look at formation. To get the best out of players, they need to play them where they feel most comfortable. Toni is a great player but he'd need to be played in the right position, with the right formation. If he wasn't, it probably wouldn't work."
Toure has won many plaudits for his performances this season, and rightly so.
The former Barcelona star has been the driving force behind City's Premier League title challenge but there is much more to his game than just power, often this season he has been the one to produce that little piece of magic when it is most needed. The 30-year-old has it all.