Derek McInnes's side were fortunate to escape with just a 2-0 loss from the first leg in San Sebastian against a Basque outfit who were simply a class above.
Aberdeen are still in with a chance of turning the tie round, but will need to significantly raise their game to even compete with the La Liga aristocrats on Thursday.
It was a difficult evening for Aberdeen, who found it impossible to live with the side that finished seventh in the Spanish top flight last campaign. But Reynolds reckons he and his team-mates will gain from their experience.
He said: "There are things we can take from the game. We won't face anything like that quality domestically this season. They are a top side and they have got top players. It's a big learning curve for us, but there were times I thought we coped well with it. But their quality showed through in the end.
"It was hard work. We knew it would be a tough tie and a step up from what we faced in the last round. It was just what we expected - their passing and movement was unbelievable. It was a tough shift. The first 20 minutes I thought we did quite well. We knocked the ball about, but they started pinching it off us and it dented the confidence a wee bit.
"We soaked up a bit of pressure but we limited them to half chances. But a couple of moments of slack play cost us. That was the disappointing thing, both goals could have been avoided. But that's what can happen at this level if you allow good players to play."
The enormous gulf in class between La Liga and the Scottish Premiership was brutally illustrated last week.
Sociedad have just forked out £8 million for long-term Celtic target Alfred Finnbogason and taking them on was always going to be a difficult task for the side that finished third in Scotland last season.
Reynolds explained: "You could see their quality shining through. They have only been back for three weeks and only played a couple of games and they are already at that level.
"You're up against top class athletes but we knew that would be the case. We showed our fitness and it was almost a bit of a leveller for us. We were sharp enough to keep pace with them but they had so much possession it was difficult for us to do much when we didn't have the ball."