Mowbray ruled out a permanent deal ahead of the Clydesdale Bank Premier League clash with St Johnstone at Parkhead.
"If he goes back to Tottenham at the end of the season all we can do is hope he enjoyed his time at Celtic and contributed some goals, which he already has done, and hopefully made some enjoyment for the supporters.
"But football is very much about finance these days and Robbie Keane is way out of our structure.
"He cost Spurs £12million. I don't think that our board are going to loosen the purse strings that much.
"I wouldn't dare tell Harry Redknapp what his best options would be, but I do know that Robbie will have benefited from playing regular football and he has shown the quality that he possesses.
"Harry has some pretty special players at his disposal and Robbie is here because Jermain Defoe, Peter Crouch and Roman Pavlyuchenko were competition for him and obviously he wanted to play. He may face similar challenges when he goes back.
"But when was the last time a Scottish club played £12million for a player? Was it Tore Andre Flo? Those days are long gone in the Scottish game, I think."