Merino completed his move to Arsenal on Thursday, though faces a month out after a shoulder injury suffered in training.
Odegaard wrote in today's match programme notes: "It's great to welcome Mikel Merino to the club. I played with him for one season at Real Sociedad when I was on loan there. He’s a great player, a great person and I have no doubt he will be a really strong addition to the squad on and off the pitch.
"He’s a leader as well, he’s been through a lot in his career, has won things with Sociedad and also with Spain now, so he brings something different. He brings a lot of quality on the ball of course, but also in the duels he is so strong.
"The number of duels he wins is incredible and on top of that, he runs so much in every game. I had a great connection with him in Spain and we played very well together, so I’m really looking forward to playing with him again.
"I spoke to him a few times when his move here started to happen. I basically just said to him that I was there if he needed anything to settle into his new club, and how much I was looking forward to getting going again with him."