Costa has been told he is not in Chelsea's plans for this season, and has made clear his preference to join former club Atletico Madrid.
But with Atletico banned from making any new signings until January and reportedly hesitating at signing Costa, the striker may be forced to look elsewhere for a new club.
Speaking at a press conference, Koeman reference his desire to bring in a new striker. When asked if that signing needed to be permanent or could be temporary, Koeman inquired, "Is that about Costa?
"Of course you like to sign players for the future, but if you can get the best one that way, then why not?
“That’s for six months, the season, two years," Koeman added, indicating he is open to the possibliity of a loan while Costa waits for an Atletico move to materialise.
“We have the possibility maybe to sign good players, but we don’t play in the Champions League – and that sometimes makes things very difficult.”Everton defeated Hajduk Split 2-0 in the first leg of a Europa League qualification play-off on Thursday.