Swann is struggling with a side injury but is expected to be fit for the first Test against South Africa at Centurion, which starts tomorrow.
“Graeme’s injury is improving and we expect him to be available for the first Test match,” coach Andy Flower confirmed.
“But with a further three matches to come after Centurion we have decided that we need a ‘like-for-like’ replacement on hand for Graeme should this be required later in the tour.”
Swann showed no signs of his injury against a South Africa Invitational XI last week, taking 6-55 and hitting an unbeaten 39 from 43 balls.
Kent spinner Tredwell, 27, was first called up for England for the 2007-8 tour of New Zealand without playing a game.
He was already in South Africa after being recalled for the one-day squad but this time Adil Rashid was preferred, limiting Tredwell’s action to the England Performance Programme, which was also stationed in South Africa.
Tredwell took 69 wickets in last season’s County Championship for Kent at an average of 26.6, and is also regarded as a useful batsman, scoring two first-class centuries for his county.
Meanwhile, South Africa are set to line-up with all-rounder Jacques Kallis and fast bowler Dale Steyn for the first Test after both were included in a 15-man squad.
Alviro Petersen, Ryan McLaren and Wayne Parnell were the players to miss out.