A former striker and fans' favourite at both clubs, the Pole has remained close to the game by working as a UEFA match delegate.
The 51-year-old - who moved to Glasgow from Legia in 1989 - had designs on returning to the Polish capital to attend the first leg of the third round qualifying tie. However, his duties instead require him to be in Spain ahead of Aberdeen's meeting with Real Sociedad in a third round Europa League qualifier.
"This was going to be the one time I could have watched Legia and Celtic play against each other and I will not be there to see it," said Dziekanowski, whose popularity at Celtic was rooted in the four goals he scored in a European Cup Winners' Cup victory over Partizan Belgrade. "As soon as the draw was made I had my plans for the first game in Warsaw and looked forward to going to the stadium to see some old friends from Celtic and their passionate supporters.
"But I work as a Uefa delegate and the letter came through the other day to tell me I was to work at the game between Real Sociedad and Aberdeen. I'm told Aberdeen are playing some very good football under Derek McInnes, but I would rather watch another Scottish team in action.
"Perhaps there is a positive in it all and that is I will not have to sit with a heart split in two during the game. Both clubs means so much to me and I have an emotional involvement. It's so hard to choose [between them], it really is."
Dziekanowski will not be able to attend the return leg at Murrayfield on August 6 either but the former Poland internationalist is certain that both legs will be closely fought. "From the performances of Legia this season and the information I have about Celtic, I think this will be a tie that goes all the way," he said.
"Legia are well organised but not dynamic. Neither side will win either game comfortably, in my opinion. It is 50-50 at the moment."
A defeat in the tie would upset the balance of support enjoyed by the Legia head coach, former Rangers player Henning Berg, though. Dziekanowski acknowledged that losing to Celtic could cost Berg his job in the Polish capital.
"There is real pressure on Berg to win the tie and then go on to win the final qualifier to make it into the Champions League," he said. "The fans are optimistic and really want Champions League football. They expect the club to move forward.
"If Legia lose to Celtic then Henning Berg's position will become very weak. He got a good result last week when they defeated St Patrick's in Ireland to get through to play Celtic. That result was so important for him.
"The amount of money on offer is also incredible. Celtic or Legia will be able to take significant steps forward if they qualify and have money to spend to improve the team. That's the scenario every coach dreams about. But it cannot be a reality for all of them. Some must cope with extreme disappointment."
n Pol van Boekel will referee Celtic's first leg against Legia Warsaw, with the Dutchman more recently acting as a fifth official in the Champions League final last season.
Van Boekel has refereed a Scottish club before, taking charge when Motherwell lost to Panathinaikos in a 2012 Champions League qualifier.
The Europa League qualifying tie between Aberdeen and Real Sociedad will be refereed by German Bastian Dankert, while Mattias Gestranius of Finland will be in charge of the tie between St Johnstone and Spartak Trnava.