Seemed like they wanted him out last minute. Plus didn't he agree to renew on a lower wage conditional to this loan. So I'd assume their hands were tied to an extent if they tried to add this clause to negotiation.
Yes, It's possible that in a limited time for negotiations this clause wasn't the most important thing to consider for both teams.
But in a different situation (for example if we would negotiate this loan 2-3 weeks earlier) and Atleti would want to include a fear clause then our only option would be to offer paying them some additional fee so he could play against them. Not sure if we could really afford or be willing to do that though. Depends on how much Atleti would want as a compensation I guess.
We did similar when loaning Eric to Girona as it happened on last day of TW so he was eligible to play againt us. OTOH with Pablo Torre loan that was negotiated early in TW we included a clause Girona had to pay us something like 200-300k IIRC if they would want him to play against us.
E: I found this article from December.
“Pablo Torre has a clause in his loan contract that does not allow us to play him vs Barcelona,” he told Cadena SER.
“However, as Eric was a last-minute move, they did not ask for the clause and he will be available.”
If Girona do want to play Torre against Barcelona then they’ll have to pay out 200,000 euros, something that looks highly unlikely as he’s yet to start in La Liga for his new side.
The two players are out on loan
www.barcablaugranes.com