Published: 2017-08-08 19:19:57 BdST
Bale was once the world's most expensive player when he joined Madrid from Tottenham Hotspur for 85.5 million pounds ($111 million), although his status in Madrid has fallen due to an injury-ravaged last campaign that saw him miss the starting line-up for the Champions League final win over Juventus.
Bale's Real future has been further cast into doubt by the club's reported pursuit of teenage sensation Kylian Mbappe of Monaco, although he is expected to start against United.
Mourinho said he would take the Wales international's absence as an invitation to lure him to Old Trafford.
"If he is not in the club's plans, that with the arrival of another player would mean he was on his way out. I will try to be waiting for him on the other side and fight with other coaches that would want him on their team," Mourinho told a news conference ahead of Tuesday's game in Skopje.
"If he's playing tomorrow, I wouldn't think of that, it would be because he's in the coach's plans and the club's plans, because he also has the motivation to continue at Real Madrid."
United have signed striker Romelu Lukaku, midfielder Nemanja Matic and defender Victor Lindelof this summer for a combined 146 million pounds as they seek to mount a Premier League title challenge after finishing sixth last season, and Mourinho has said he would like one more signing.
The Super Cup is the only European trophy Mourinho is yet to win as a coach, having lost the 2003 and 2013 editions while with Porto and Chelsea respectively. United have not lifted the trophy since 1991, and the Portuguese coach said his side were the underdogs to double Champions League holders Real.
"We are going to try but the difference between the Champions League winners and Europa League winners is obvious. There is a big difference of quality but we believe it's possible," Mourinho said.
The coach also raised concerns about the scorching temperatures in the Macedonian capital, which have led tournament organisers UEFA to permit water breaks during Tuesday's game.
"I knew the weather was like this and since we got back from the United States. In Madrid they have training sessions with the hot weather so must be more adapted than we are but we have to play and enjoy a special moment," he said.
"It is not often a player has the chance to play a Super Cup unless you are like Madrid and Barcelona winning regular European trophies."