The Japan international has played a total of just six minutes in the current campaign due to a pair of knee injuries, the latest of which he will reportedly need an operation to correct, one that could render him unavailable for the rest of the season.
While Tomiyasu has had a torrid time fitness-wise in North London, he is a trusted performer for Mikel Arteta when fit and was rewarded with a new contract until 2026 - with the option of a further 12 months - midway through the 2023-24 campaign.
However, the 26-year-old's latest injury blow could scupper Arsenal's hopes of selling him this summer, meaning that he could depart for nothing at the end of next season if his 12-month extension is not triggered.
Even though that would mean Arsenal losing their £17m investment for nothing, Watts believes that is the only viable option, saying: "I would be very surprised if they took up the option on it, because why would you?
"Pretty mad" to take up Tomiyasu contract option
"As much as we all like him and they all like him, it's a business point of view. It seems pretty mad that you'd take up that option. I think it's just the focus just has to be on getting him fit, getting him ready and seeing if you can get something out of him next season.
"They haven't been able to fix his knee issue. It looks like he might have to go under the knife again. And if he does, then there's no way we're going to see him again this season. They're not going to sell him in the summer because who's going to buy him when he hasn't played for a whole season?
"All we can do is then hope he does get this sorted, he can come back in the summer or for pre-season and can still offer something to Arsenal in the final year of his contract."
Arsenal memorably pipped North London rivals Tottenham Hotspur to the signing of Tomiyasu in 2021 as their bitter foes instead swooped for Emerson Royal, who failed to impress in the Premier League.
In contrast, Tomiyasu immediately won over the Emirates crowd with his defensively sound displays both at right and left-back, registering two goals and three assists in 30 games last season and ending 2023-24 as Arteta's first-choice on the left-hand side.
However, the versatile defender has been beset by fitness problems ever since his arrival from Bologna and has missed 82 matches for club and country while representing Arsenal, just two fewer games than he has actually played for the Gunners.
"Not a mistake to give Tomiyasu new contract"
Nevertheless, Watts does not think that Arsenal will be looking back on extending Tomiyasu's contract with regret, adding: "At the time he signed that new contract, I was all for it. Tomiyasu is a fantastic, fantastic player who gives you so much. He can play right back, centre back, left back, and he can play all of those positions equally well.
"The whole Tomiyasu thing is just such a shame, and I feel really sorry for him. In my dealings I've had with Tomiyasu, he's the nicest guy. He's so respectful. He's so dedicated to what he does. I know this will be killing him not being able to play and not being able to help the team.
"I see some really horrible comments on social media about it like 'get rid, waste of space.' I just think it's so incredibly harsh. No one will want to play more than Tomiyasu does. And when he does play, he's such a good player.
"So I don't really think they'll look at it as a mistake. I think they protected themselves by only giving him that short term deal, which made a lot of sense to me. I know he's had his injury problems, but no one could have predicted he's going to play six minutes and that's it this season."
However, Tomiyasu is now Arsenal's only defensive absentee after Ben White was back on the bench for the 2-0 win over Leicester City at the weekend, and the remainder of Arteta's concerns lie in the final third.
Gabriel Jesus and Kai Havertz will not play again this season, while Gabriel Martinelli and Bukayo Saka will be out for weeks more, forcing Arteta to send on Mikel Merino as an emergency number nine against Leicester.
Watts: 'Arsenal must use injury situation as learning curve'
The Spaniard wrote his striker's hero arc with two goals, but given Arsenal's shortages in attack while their defence remains largely intact, Watts believes that the Gunners' transfer chiefs must use their current situation as a learning curve.
"They've been without Tomiyasu for that long, Ben White's been injured for so long, but Arsenal haven't struggled because they've protected themselves so much," he added.
"They have so many good defenders in their squad that you can cope with those injuries because you can just move players around, and they've had loads of players out in defence. And yet that's never really been an issue because their squad has been built so well to protect themselves.
"It just seems so mad that you've got at one end of the pitch, you've done it so well. And yet at the complete other end of the pitch, you've left yourself so exposed. It's got to be a learning curve, I think, for the squad building.
"And this summer will be the summer that we see Arsenal improve massively in attack and strengthen massively in attack. But by then, it could be too late for this season anyway."
Watts also offered his take on whether the Gunners could pursue a shock deal for free agent Diego Costa to solve their offensive crisis ahead of Saturday's Premier League showdown with West Ham United.
Written by
Ben Knapton