Koeman, who managed Wijnaldum as Netherlands head coach, discussed the club's failure to sign the midfielder, who he praised for having a “great sense of space".
“Gini has a great sense of space," Koeman told AD. “He can get to the goal fantastically well from midfield, he could really add something to the team.
“But the financial situation was known to the club.
"His position ultimately had less priority than, for example, the right-back or the striker position."
Barcelona can sign Wijnaldum on a free transfer next summer. They will be able to begin negotiations in January.