Masahiro Tanaka placed on 10-day disabled list
Tanaka, 28, has made 23 starts for the Yankees this season, posting a 4.92 ERA with eight victories and a stellar 141 K/33 BB ratio.
Over his last nine starts, Tanaka has shown the form that made him a fringe Cy Young candidate last season, pitching to a 3.00 ERA and limiting batters to a .214 batting average over that span.
Gallegos, 25, debuted for the Yankees on May 12, and has made nine appearances over the course of this season in the Majors. He's allowed nine earned runs in 11 1/3 innings pitched, but in Triple-A Gallegos has pitched to a sparkling 1.69 ERA over 24 relief appearances.
In 2016, Gallegos finished the year with a 1.27 ERA at both the Double- and Triple-A levels, while demonstrating a knack for striking out his opponents (106 K/17 BB).
The news of Tanaka comes just one day after another Yankees starter, CC Sabathia, was also placed on the 10-day D.L. with inflammation in his right knee.
The Yankees can clinch this weekend's series against the Red Sox with a win Saturday, as Luis Severino squares off against Drew Pomeranz at The Stadium.