The troubled euro zone will become Deutsche Telekom's main source of income if it succeeds in completing the sale of T-Mobile USA for $39 billion to AT&T next year, with Germany alone accounting for more than half its business.
"The Europe segment (Greece, Hungary, Croatia, etc.) is at risk to be affected by a global economic slowdown and economic disruptions in the individual countries," said analyst Thomas Friedrich at UniCredit Bank.
All eyes will be on Deutsche Telekom's biggest operation outside Germany, its 40 percent stake in Greek telecom group OTE, which will also release results on Thursday.
Deutsche Telekom bought its first stake in the Greek operator in 2008, hoping to benefit from growth in southeastern Europe but a year later was already forced to write down 1.8 billion euros ($.5 billion) on the investment.
Chief Financial Officer Timotheus Hoettges said in August he did not foresee another writedown at the moment but could also not rule out any future ones.
British peer Vodafone on Tuesday announced an impairment loss of 450 million pounds ($724 million) in relation to its Greek business, citing tough conditions.
Deutsche Telekom has an option to increase its stake but Chief Executive Rene Obermann has questioned whether it makes sense to invest further in the company.
The Greek government would like to sell its remaining stake in OTE, which is expected to report a 23 percent drop in third-quarter net profit on Thursday.
Deutsche Telekom's third-quarter earnings before interest, tax, depreciation and amortization (EBITDA), excluding special items from continued operations, are expected to fall 4.3 percent to 3.82 billion euros.
Deutsche Telekom expects to generate 14.9 billion euros in core profit this year from its German and European operations and 4.2 billion from T-Mobile USA, with free cash flow of at least 6.5 billion.
Its shares have lost 8 percent so far this year, in line with the STOXX Europe 600 Telecommunications index, but outperforming the German blue chip index which is down 16 percent.
(Additional reporting by Georgina Prodhan; Editing by Helen Massy-Beresford)