The 23-year-old was left on the substitutes’ bench for the Scottish Premiership encounter between the two sides at Celtic Park.
Bitton eventually came on just before the hour mark when he replaced Anthony Stokes, but he failed to prevent the Bhoys from suffering a shock 1-0 defeat.
Deila has now explained why the 23-year-old Israel international defensive midfielder did not feature against St. Johnstone from the opening minute.
“Because he has been playing a lot of games and he's not used to it, and so he's more ready for weekend,” the Norwegian told Celtic’s official Twitter account when posed the question.
RD on why Nir Bitton didn't start: “Because he has been playing a lot of games & he's not used to it & so he's more ready for weekend." (MH)— Celtic Football Club (@celticfc) March 4, 2015
Bitton is an important player for Celtic, and Deila was right in giving the former FC Ashdod star some 'rest'.
Perhaps with the 23-year-old in the team, the Glasgow giants may not have lost the game, but that is purely hypothetical.
Now that Bitton got some ‘rest’ in midweek, it is imperative that he starts for Celtic against Dundee United away from home this weekend.
It is the quarter-finals of the Scottish Cup on Sunday, and Deila needs his best players at Tannadice Park.