Walcott went close to scoring against his former side in the first half but was denied by a last-gasp challenge from Shkodran Mustafi and as the game entered the final third with the visitors still 4-0 down and with no realistic chance of a comeback, Allardyce chose to give his latest recruit a breather.
He said: “Going back to Arsenal was a place where Theo wanted to come and do well.
“I always thought he'd get a good reception for what he'd done at Arsenal but when he went out on the pitch he really wanted to go out and shine.
“He got very little service and there was very little quality to enable him to do that.
“I protected him in the end because we weren't going to come back and get a result.
“The last thing I wanted him to do is pull a muscle through fatigue because he hasn't played many games this year and he's our top player for physical output in terms of speed and the distance he covers.
“There was no point in risking him any further."