Dejagah, alongside Sasha Riether and Lewis Holtby, has played under Magath before and was a first-team regular until Fulham snapped him up from Wolfsburg in 2012.
The Iran international winger was initially favoured by Magath's predecessor Rene Meulensteen but had been overlooked recently.
Dejagah could come into the side again when the German boss picks his first team to face West Brom on Saturday, having promised to concentrate on a core group from what he described as an oversized squad.
"I have to cut down the number of players in the team," said the Fulham boss.
"If we have too many players we have too many influences. Sorry for that but it's the only way to concentrate on the next game. If they cannot accept it I cannot use them."