The game against Espanyol on Sunday proved to be a landmark for both Caulker and Rodriguez.
Caulker made his first appearance as a Southampton player after joining on a season-long loan from QPR while Rodriguez was handed his first start since recovering from a long-term knee injury.
After the game, Koeman admitted that the duo were a bit rusty but insisted that the two Englishmen will soon adapt to his Saints game plan.
"Maybe a little bit in the beginning he (Caulker) needed more adaptation to the players and the team," Koeman told the club's official YouTube channel.
"It's normal, he's had just two days with the squad, but he reached a good level.
"It was Jay's first start for a long time in St Mary's, you can see at certain moments he's not what he was, but that's normal after a long time.
"He needs minutes and time to come back to that level. He still showed his quality, he scored a great goal and that will give him the confidence he needs."