The Germany captain moved to Stamford Bridge on a free transfer from Bayern Munich in 2006, but has struggled to replicate the form he showed in the Bundesliga for the Blues.
And Matthaus, who won 150 caps in a 20-year international career for Germany, believes Ballack could soon be discarded by Chelsea.
"At Chelsea Ballack is just present rather than right in the thick of things. He is a nominal player at the big London club - that is not an insult," Matthaus wrote in Sport Bild.
"The squad is packed with top stars. To establish yourself as a leading player there is hard. Ballack has not managed it.
"He is always in the first team. The question is only: For how much longer?"