Sprint parent SoftBank has eased up on its investment as shares of its U.S. carrier have languished, BTIG Research noted this morning.

“SoftBank is in another extended pause in the purchase of Sprint shares,” Walter Piecyk of BTIG wrote on the firm’s blog. “Its last reported purchase was over a week ago on 12/5. We previously thought SoftBank would stabilize Sprint’s stock at ~$6/share, but its purchase activity has been less aggressive over the past month as the stock traded first below $6 and then below $5.50/share for three days before rebounding the past three days.”

Shares of the fourth-largest U.S. carrier were down 16% after merger talks with T-Mobile fell through, BTIG reported, and the stock was trading at $5.57 midday Friday, down more than 1% from its price when the market opened.

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SoftBank CEO Masayoshi Son said last month he planned to increase his company’s stake in Sprint from 83% up to 85%, butting his investment up against the threshold that would trigger a public offer for all the remaining shares. But the downturn in Sprint shares hasn’t spurred the Japanese conglomerate to up its ante over the last 10 days, Piecyk observed.

“Sprint and SoftBank have not provided any indication on why buying has been suspended,” he wrote. “We estimate SoftBank can still purchase up to 54.5 million shares before hitting the 85% threshold that would trigger a tender for Sprint. If SoftBank elects not to exercise its warrant to purchase Sprint stock at $5.25 per share (a reasonable choice if the stock drop bellows this level), it would have an incremental open market buying power of 8 million shares. At SoftBank’s current buying volume of ~1.9 million shares per day, it would take 28 trading days to reach 85% ownership, which would extend its purchases into late January 2018, at a minimum.”

Sprint’s genuine value has become a matter of intense speculation among analysts and investors in recent months. The carrier has made major strides in cutting costs and clawing back market share, but some believe the company’s real worth lies in its 2.5 GHz spectrum holdings. Indeed, MoffettNathanson predicted in October that shares of Sprint would plummet to less than $3 if the tie-up with T-Mobile were to fall through—but that prediction has obviously not come to pass.