Berdych returns to ATP-WTA Portugal Open after nine years
Czech Republic's Tomas Berdych, pictured during a match at the Monte-Carlo ATP Masters Series tournament, in Monaco, on April 17, 2014 - by Jean-Christophe Magnenet
Wawrinka, who added the Monte Carlo Masters title last week to his Australian Open trophy, withdrew and is next due to play in Madrid in a week. Wawrinka cited fatigue for his pullout.
Berdych, who will play as a wild card entry, tweeted his pleasure at making a return to the event where he played his one and only main draw match nine years ago.
The sixth-ranked Czech can use the week outside the capital of Lisbon as valuable clay training after winning one round in Monte Carlo and then going out in the third round to Guillermo Garcia-Lopez.
Canadian Milos Raonic will take the second seeding with the newest member of the ATP top 10 looking for improvement after the number nine lost last week to Wawrinka in the principality.
Raonic played the event in 2011, losing a semi-final to Fernando Verdasco as the Canadian retired with a back problem.
The top four men's seeds get byes, with Berdych starting against the winner from Somdev Devverman and Australian Matthew Ebden.
Raonic will face either Aleksandr Nedovyesov or Pablo Cuevas.
On the WTA side of the draw, Spain's Carla Suarez Navarro takes the top seeding ahead of Canadian Eugenie Bouchard, the Australian Open semi-finalist.
Australian Samantha Stosur, once a regular member of the top 10, comes in as third seed standing 19 in her Portugal debut.
Roberta Vinci of Italy is fourth, ahead of Estonia's Kaia Kanepi, Berdych's one-time girlfriend Lucie Safarova (sixth) and the Russian pair of veteran Svetlana Kuznetsova and Elena Vesnina.