By Axel BuggeLISBON (Reuters) - Portugal clinched a deal on ambitious labor market reforms this week and carried out its biggest debt sale since seeking a 78-billion-euro bailout, but the challenges for the second-most risky country in the euro zone may be shifting up a gear.Undermining the glow of Lisbon's achievements is the rapidly rising market concern that Portugal is the next potential candidate to default in the euro zone after Greece -- a point that is fast becoming clear as Athens approaches the end of its debt restructuring talks."Portugal is obviously the next in the line of fire," said Michael Cirami, a portfolio manager at U.S. investment managers Eaton Vance. "Portugal is unlikely to go unnoticed whether they strike a deal or not (on Greek debt restructuring)."The concerns were clearly borne out this week as Portugal's bond yields rose virtually without interruption, to all-time highs, despite the issuance of 2.5 billion euros of short-term treasury bills on Wednesday at slightly lower yields.The country's 10-year yields rose to almost 15 percent on Thursday and hovered around 14.80 percent on Friday. Five-year credit default swap prices implied the market was pricing in a 66.8 percent chance of a Portuguese default.The sharp rise in bond yields was partially triggered by Standard & Poor's downgrades of European countries last week, which left Portugal as the second euro zone country to be rated "junk" by all the main rating agencies, along with Greece.
Read more: Has Portugal's debt default clock begun to tick? - Yahoo! Finance