The Yankees’ window for being the only team to talk to free agent CC Sabathia closes at midnight Friday evening. After that, the veteran free agent lefty can negotiate with any other team.

Though there is interest from the Yankees and Sabathia to continue the relationship for an 11th year, allowing other clubs into the action creates a sense of the unknown.

A year ago, when Sabathia was coming off a very similar season (14-5; 3.69 ERA; 148 ²/₃ innings; 27 starts) to this past one (9-7; 3.65 ERA; 154 innings; 29 starts) the Angels and Blue Jays attempted to lure him away from The Bronx. Ultimately, Sabathia signed a one-year deal for $10 million to remain a Yankee.

All free agents can start negotiating with teams other than the one they played for this past season at 12:01 a.m. Saturday. The Yankees are expected to make a serious pitch to lefty Patrick Corbin and have entertained thoughts of bringing left-hander J.A. Happ back. That would leave room for the 38-year-old Sabathia in a rotation that will have right-handers Masahiro Tanaka and Luis Severino.

Sabathia, who told The Post’s Dan Martin late in the season that 2019 would be his last, expressed a desire to remain with the Yankees on Oct. 17 in a telephone conversation with The Post.

“The way it ended was tough. There were so many expectations, to end like that was tough,’’ said Sabathia, who gave up three runs and five hits in three innings of Game 4 against the Red Sox in the ALDS that resulted in a season-ending, 4-3 loss a year after the Yankees pushed the Astros to seven games in the ALCS. “It’s a young team and we needed to go through that experience to make it a better team and get over the hump and win a championship. And it will happen.’’

With him?

“Who knows, but I still feel good and can help this team for sure,’’ said Sabathia, who has a 246-153 career record and 2,986 strikeouts.

In other developments, clubs have until 5 p.m. Friday to make qualifying offers to free agents who played for them this past season. The Yankees aren’t expected to make the offer, which is for $17.9 million to David Robertson and Sabathia. The Yankees can’t make the offer to Zach Britton, J.A. Happ, Andrew McCutchen, Adeiny Hechavarria and Lance Lynn because they were dealt to the Yankees during the season.

As for Sabathia, the same day general manager Brian Cashman said he was looking to deal Sonny Gray, the veteran lefty underwent arthroscopic surgery on the right knee. He has ditched the crutches while rehabbing the hinge and is looking forward to an offseason tradition of throwing a football with his oldest son, Carsten Charles III, who is known as “Little C.’’ He said he would begin throwing a baseball in late December or early January.

Sabathia told The Post late in the regular season he will pitch in 2019 and retire. It could be elsewhere, though last month it sounded like he would prefer to remain in The Bronx and win a second World Series as a Yankee.