Release clause will increase from €18m to €25m.
Manchester United are without a win in their last five matches, which includes a defeat against Wolfsburg.
Vice-president Ahmet Nur Cebi says a fee and a contract are still to be agreed with the Gunners.
Sporting director Robert Fernandez is confident the reigning champions will go through the next round.
Spaniard suffered a rupture of the external knee ligament during the 1-1 draw against Norwich City.
England international also paid tribute to Olivier Giroud.
Chelsea meanwhile will clash with PSG for the third year running.
Manchester United are without a win in last five matches played in all competitions.
Savic failed to impress at City but became a force in Serie A.
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Wenger praised striker after his hat-trick took Arsenal through to the next round of the Champions League.
The French boss says he already has a great striker in Olivier Giroud.
The Gunners visit Villa Park following their impressive 3-0 victory at Olympiakos.
The former Manchester United striker has been out of action since April.
Gunners need to win by two clear goals to qualify for the last 16 of the Champions League.
Gnabry has made just one appearance for the Baggies this season.
Reports suggest the Gunners are considering a January move for the PSG midfielder.
Ramsey and Flamini to start in midfield in the absence of Cazorla and Coquelin.
Manuel Pellegrini is without six key players in pursuit of top spot in Group D.
Debuchy says he would consider moves to another English side or back to France.
Wenger is reportedly considering both players to bolster the Gunners attack in January.
Real Sociedad are contemplating a £22m bid from the MLS, which the Gunners will earn a cut of.