SoftBank Group Corp. is waiting to hear back from Deutsche Telekom AG on an eleventh-hour bid to save a merger between Sprint Corp. and T-Mobile US Inc., as the chances for a deal dwindle fast, according to people familiar with the matter.

The Japanese company is expecting Deutsche Telekom to make a final proposal this week that will include how many Sprint shares it’s willing to accept for each T-Mobile share, said the people, who asked not to be identified as the detail aren’t public.

SoftBank, led by Chairman Masayoshi Son, has signaled it is holding out for an exchange ratio of less than 8 Sprint shares per T-Mobile share, they said. The current exchange ratio, based on Tuesday’s trading, is more than 9. 

Even if Deutsche Telekom offers an appealing exchange ratio, Son has reservations about relinquishing control of Sprint given his desire to dominate a future internet-connected world, one of the people said. SoftBank has been negotiating how to keep Son as a decision-maker for the combined company, including naming the billionaire as co-chairman, the person said.

Deutsche Telekom shares fell as much as 3 percent in early Frankfurt trading, the steepest intraday decline since June 27. They lost 2.9 percent to 15.19 euros at 9:27 a.m. local time.

A spokeswoman for Sprint declined to comment. Representatives for Deutsche Telekom, SoftBank and T-Mobile didn’t immediately respond to requests for comment.

Talks hit a serious snag in the past few days as the companies clashed over details from valuation to control of Sprint’s U.S. wireless business, people familiar with the matter said Monday. While merger talks have been under way for months, SoftBank board members raised their concerns in the last few days because it’s now a make-or-break moment, with the sides very close to a deal, the people said.

Sprint shares rose 3.15 percent to $6.54 in New York Tuesday, valuing the company at about $26 billion. The stock closed down 9.3 percent on Monday. T-Mobile were little changed at $59.77.