An overhaul of the playing squad at the Bernabeu is expected in the summer with the LaLiga side struggling, now sat in fourth place in the league and 19 points behind Barcelona.
The former Brazil and Real Madrid star believe the La Liga giants should go after his countryman.
Zinedine Zidane's men are aiming to win the European crown for a third straight year and host PSG in their first leg on Wednesday.
They take on PSG in the Champions League second round first-leg on February 14 in desperate need of a win, with Zinedine Zidane's side struggling domestically.
Robert Lewandowski to Real Madrid?
"That Madrid is going through a low in the league at the moment is, in my opinion, quite normal", he added. "Sooner or later, PSG will win the Champions League", Xavi said. It will be a very strong tie, although I think the favourite is PSG, due to their form. You need a really good mix between young and old, between experienced and hungry players.
Lewandowski was on target as Bayern beat Paderborn 6-0 to move into the DFB-Pokal semi-finals on Tuesday, with their next match coming at home to Schalke in the Bundesliga on Saturday.
Ronaldo, who spent more than four seasons at Madrid, said his former club were always looking to sign the best, and that included Neymar.
One of the deadliest forwards in European football is reportedly dreaming of a transfer to 12-time UEFA Champions League winners Real Madrid. "I'm sure that we will see that victory in the near future".