Gary Caldwell admitted he was "bitterly disappointed" after Celtic suffered another UEFA Champions League defeat on the road to Benfica.
Oscar Cardozo scored the only goal of the game in the 86th minute to leave Gordon Strachan's men bottom of Group D.
The result means Celtic have not won in 14 attempts away from home in the group stage and have it all to do to lift themselves for the re-match at Parkhead in a fortnight's time.
Caldwell told Sky Sports: "I think we deserved a point - we set our stall out to defend and we did well for long periods. Artur Boruc is fantastic, he makes great saves at big moments.
"The defence, midfield and attack all worked hard and it's bitterly disappointing to lose it at the end.
"I think (Benfica) are a good team, but coming to Parkhead is a different game. I'm sure they won't be looking forward to coming to our home ground."
Hoops skipper Stephen McManus added: "It's very disappointing to be honest but we need to pick ourselves up and get ready for the next challenge.
"When you play away in the Champions League they're always tough games. We set our stall out and we felt we deserved at least a point."