No wedding date has been set for the couple, who have been dating for about a year.
Fisher, 29, recorded his 300th career point for the Senators in their 4-1 win over the Minnesota Wild on Saturday. Fisher had an assist on Anton Volchenkov's goal in the first period.
Asked by The Associated Press last month what Underwood's family thought of Fisher, the 26-year-old singer said they were supportive.
"They love me and I would hope my parents would think we raised a good, smart girl, so she's going to do the right thing no matter what it is," she said.
Days before the CMA Awards in early November, Underwood did not know whether she would be spending the holidays with Fisher.
"Christmas, I don't know. We haven't really thought that far ahead. We kind of take it one week at a time," she said then.
Underwood has kept her relationship largely under wraps, but she gave Fisher a very public shout-out in the liner notes of her current album, "Play On," that was released Nov. 3. She wrote, "Thank you (No.) 12 (referring to his jersey number.) You are the most amazing addition to my life! You are such a wonderful person and have had such an amazing hand in the building of this album and in the growth of me as a person. I love you so much! You make my life better in every way!"
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