Werner (hamstring) and Lukaku (ankle) were both forced off before half-time in their 4-0 Champions League win over Malmo at Stamford Bridge.
Christian Pulisic will also be unavailable for their game against Daniel Farke's side as the forward continues with his recovery from an ankle injury.
To make the question a longer one, how is Pulisic too? They are all out tomorrow and probably the Southampton game and then we will see.
I don't think it makes sense to go into speculation about how long [the players will be sidelined for] because you never know. Things can be shorter than expected or longer than expected.
What I can tell you for sure is they are both in treatment, positive and not worried but out of the next two games for sure
Chelsea's head coach said he did not regret playing Lukaku against Malmo despite stating before the game that he thought the Belgian striker was overplayed during the international break.
The injury setback comes as a blow for Lukaku who has begun life back at Stamford Bridge in fine form, scoring three goals in seven Premier League games since returning to the club from Inter Milan.
Mentally he is a bit overplayed but that does not mean we have to rest him.
Chelsea have a busy playing schedule with five games in the space of 15 days and Tuchel will need to adapt his starting XI on Saturday.
I hope we have the better end tomorrow. We will do everything we can to get the win.