There are a number of options under which the contract will not come into effect, the person, who is familiar with the contract, told Reuters on Monday.
Deutsche Telekom declined to comment on the matter.
The U.S. government last week sued to block AT&T's purchase of T-Mobile USA, a deal that would vault the combined company above Verizon Wireless as the No. 1 player in the United States.
As part of the AT&T deal, Deutsche Telekom secured a breakup fee comprising $6 billion in cash and other assets should regulators reject the deal.
Under its agreement with Deutsche Telekom, the deal is only valid if the acquisition receives regulatory approval within a certain timeframe, the source said on Monday.
Also, the agreement could become invalid if regulatory conditions for the sale push the value of T-Mobile USA below a certain level, the person said.
(Writing by Maria Sheahan)