The 24-year-old Danish international, who spent last season on loan at Roma after falling out of favour with Felix Magath, still has one year remaining on his contract.
Kjaer returned to the club last summer and went on to make 20 starts in the Bundesliga, but Allofs said that his place in the team cannot be guaranteed.
"I have had a chat with Simon Kjaer about his situation at the club and of course, it's not to Simon's satisfaction to not play regular first-team matches," he told German magazine Kicker.
"This may well, in the end, lead him to make a change."
Kjaer, who joined the Wolves from Palermo in 2010, has previously been linked with Liverpool and Newcastle United.