Wolfsburg have been urged to test Chelsea's resolve by making a move for forward Andre Schurrle during the final week of the January transfer window by former manager Felix Magath.
The 24-year-old has made just five starts in the Premier League this season and has been linked with a £20m return to the Bundesliga just six months after winning the World Cup with Germany.
Chelsea manager Jose Mourinho has denied any interest in selling players during the January transfer window but Magath, who was in charge at Fulham last season, wants Wolfsburg to prove their big-club mentality with a late bid during the final days of the window.
"With a transfer as huge as a Schurrle, one you could send out a signal to the competitors," he told Goal.com.
"The rumours have been circulating for a while now and the timing now is just right. I am confident they can become a serious rival for Bayern in the long term.
"With Kevin de Bruyne, they already have an exceptional player from Chelsea. If Schurrle really joined, the squad's quality would rise again and they would increase their chances to stand their ground on a sporting level."
Schurrle missed the 4-2 FA Cup fourth round loss to Bradford City with a back injury but is likely to be the subject of intense speculation regarding his future as the week progresses.
Mourinho has maintained Chelsea will be reactive rather than proactive during January and says only huge offers for his players will see the club make any alterations.
"The club does not move," he said last week. "Our desire is to keep the same squad which reflects that we are happy with the players that reflect that we are happy with the work we did in the summer.
"It reflects the trust we have in the group and if possible we don't want to be involved in the transfer window. If we have to be it's because somebody pushed us with some interest in our players, some offers for our players."