The 22-year-old defender has been one of the most important players for Celtic in recent seasons and is one of the first names on their team-sheet.
Ajer has been linked with a move away from Celtic since last summer and Solbakken believes the defender needs to depart the Scottish giants to further develop and be challenged.
The Norway boss is not keen to comment on the quality of the Scottish league, but feels Ajer has outgrown the Sottish Premiership and looks like a senior player taking on youngsters.
He wants Ajer to be challenged more in every aspect of his defensive game and is keen to see him play at a higher level.
The Norway coach told Norwegian daily VG: “I have told him on the phone couple of times. In some matches he plays in Scotland, he looks like a senior playing at youth level.
“It’s of course because he is good, and this is not a criticism of the Scottish league, but he needs to be challenged more on making decisions, on speed, on physics and everything.
“If I were him, I would try to get to a higher level.”
Ajer has 19 international caps to his name with Norway and has been linked with a host of clubs, including AC Milan.
