The 65-year-old indicated the Arsenal attacker's absence forced him into making some late additions to the squad, while he assured the Chelsea forward's illness is not as severe
The Three Lions' manager has handed Southampton's Adam Lallana and Liverpool starlet Raheem Sterling their first senior call-ups, with Tottenham's Jake Livermore also joining the squad.
The 65-year-old suggested that he is covered for the defensive injuries sustained before and during the 5-0 win over Moldova, but that the recent problems in attack have forced him to strengthen the group of players, although he indicated the new faces may not be given a chance in the team just yet.
The former West Brom boss told reporters: "We were at the limit when we lost John Terry and Ashley Cole but now that Theo Walcott has had to go home and Daniel Sturridge is still being monitored, [although] we think he's going to be ok, it was a good opportunity to invite some younger players to come in and be a part of the atmosphere.
"We have enough players to deal with the game. But it's good when you have a chance to invite these younger players to come and be around the team for a short period of time.
"Theo has picked up some sort of virus or bug because he was quite violently ill last night. Daniel actually trained yesterday with these stomach cramps and complained of them but he still got through the training session.
"But today he woke up with the same sort of cramps, although [he was] slightly better I believe the doctor advised us to keep him out of training and see how things are when he wakes up tomorrow. But the doctor is quite confident he's going to be ok."
The national team head coach assured supporters that Walcott was sent home as soon as the illness was discovered to avoid the bug spreading, with the west London outfit's striker also isolated, but did not rule out the possibility of further problems.
He added: "That was one of the reasons why we were quite anxious to get Theo back home as soon as possible and of course we've kept Daniel away from the other players both last night and today.
"The reason we've called up some extra players in just in case, because you never know. You could wake up tomorrow and one or two other players are suffering from this virus, but we hope not."