"Blake and Kendall have been cooling off recently, but they're not officially broken up," a source told PEOPLE.
However, Griffin was seen with a mysterious woman in Los Angeles over the weekend. An onlooker told PEOPLE that they were "giving off couple vibes."
"At one point, she put her hand in his lap, where he held her hand there for about five to 10 minutes or so," the witness told the magazine.
The person said the 28-year-old Griffin and the mystery woman were "very low-key together, and their holding hands looked entirely natural... They looked like they were really comfortable with each other, and they were definitely not calling any attention to themselves and the little bit of PDA that they shared."
The 22-year-old Jenner and Griffin have been dating since August. In July, Griffin and fianceé Brynn Cameron, with whom he has 4-year-old son Ford and 1-year-old Finley, called off their engagement.
"Blake and Brynn broke up in July," a source told Us Weekly in September. "They ended things on good terms and they are still friends while raising their son and daughter."
Since they started dating, Jenner and Griffin have been seen together frequently, with Jenner catching Los Angeles Clippers games courtside. They went out to dinner the night before Jenner's 22nd birthday in November.
In December, Jenner went to Griffin's comedy show in Hollywood to support his Team Griffin Foundation.
"Kendall is very happy with Blake," a source told PEOPLE in November. "They started out more like friends, and then it was very casual. But it seems more serious lately. When they are not together, they keep in touch over the phone. Her family has accepted Blake. They are spending time getting to know him."
Griffin has played for the Clippers since he was drafted in 2009. He has played in 26 games so far this season, averaging 22.2 points per game. He suffered a scary concussion during the Jan. 6 game against the Golden State Warriors. He missed the Jan. 8 and Jan. 10 games, but returned to the court on Jan. 11.0comments
As for Jenner, she just became the new face of the Italian leather brand Tod's on Monday.
Photo Credit: Instagram / @Kendall Jenner