After reviewing several sources, this claim seems likely to be true, but we can not be absolutely certain.
Lemon made comments about former South Carolina Governor Nikki Haley saying on air, "Nikki Haley is not in her prime, sorry. A woman is considered to be in her prime in her 20s, 30s and maybe her 40s." according to USA Today.
While Lemon had a planned day off on Saturday, he was originally scheduled to be on the air Monday before the comments were made. A schedule sent out Sunday afternoon revealed he would be replaced for Monday's show according to the Huff Post and The Daily Beast's Confinder. While it can not be certain that this is the reason he was benched from Monday's show, it seems plausible.
A CNN spokesperson said, "He’s been chased by paparazzi all weekend. He’s been under attack. He’s not ready to go back on air," according to the Huff Post article. CNN Lead Chris Licht also made comments on the situation, "His remarks were upsetting, unacceptable, and unfair to his co-hosts, and ultimately a huge distraction to the great work of this organization,”
https://news.yahoo.com/don-lemon-apologizes-saying-nikki-143532540.html
https://news.yahoo.com/don-lemon-taking-monday-off-035736661.html
https://www.thedailybeast.com/don-lemon-cut-from-monday-lineup-of-cnns-this-morning-insiders-say