Idea Cellular shares fell nearly 6 per cent on Thursday on a report that India’s third biggest telecom operator may spend nearly $1.3 billion (Rs 8,650 crore at $1=66.55 rupees) to buy spectrum in upcoming auction.

“Idea may add more data capacity in four circles and we see a potential spend of $1.3 billion in the upcoming spectrum auction by the company,” the Economic Times said, citing an HSBC analyst.

Idea Cellular has so far not disclosed its investment plans.

Analysts said Idea Cellular’s aggressive capex plans are a worry because the company is already heavily indebted.

Idea Cellular had a total debt of around Rs 38,000 crore as of March 31, 2016. The telecom operator’s interest expense rose from Rs 931 crore in FY15 to Rs 1,798 crore in FY16.

The upcoming spectrum auction is scheduled to take place around mid-July. Rating agency Fitch earlier said that steep base price of Rs11,485 crore/unit for upcoming spectrum auction could exert further pressure on participating telecom companies’ balance sheets and cash flow.

As of 12.20 p.m., Idea Cellular shares traded 4.76 per cent lower at Rs 114.15 apiece compared to 0.68 per cent gain in the broader Sensex.

The slump in Idea’s shares also weighed on other telecom stocks. Bharti Airtel fell 1.5 per cent while Reliance Communications edged 0.50 per cent lower.