Cameroon's preparations for next month's World Cup took a knock when the Africans fell 2-1 to Paraguay in a pre-tournament friendly in Kufstein on Thursday.
Volker Finke's men had secured a 2-0 win over Macedonia in Austria earlier this week as they build towards the World Cup, which they begin against Mexico on June 13.
But they were trailing early on Thursday after forward Oscar Romero put the South Americans ahead after just four minutes with Malaga striker Roque Santa Cruz netting a second after 68 minutes.
Mainz striker Maxim Choupo-Moting, who also scored against Macedonia, pulled one back 15 minutes from time for Cameroon who are reportedly locked in a battle with their federation over bonuses for the tournament.
"We're in the final phase of World Cup preparations. These two matches were very important," said Finke.
"A loss in a friendly warm-up match isn't a catastrophe though."
The Africans are in a tough World Group Group A with hosts and favourites Brazil, Croatia and Mexico as they bid to qualify for the knockout stages for the first time since 1990.
But with their provisional 28-man squad to be cut to 23 by June 2 they showed problems in defence with Nicolas N'Koulou and Joel Matip in a central role, supported by Allan Nyom and Gaetan Bong on either side failing to provide the necessary guarantees.
"I've seen a lot of things which will allow me to make my final selection," said Finke.
"Every loss hurts, we don't like it, but it's a loss on which we can work."
The German coach said he had been particularly impressed by young Lens striker Edgar Salli, 21.
"He had a game which I really liked," he said. "Every player had a chance to show his physical and mental form.
"Against Germany we're going there for a result. I'm going to try and get an idea of who the final 11 will be."
Samuel Eto'o, who remained on the bench Thursday as planned, is expected play at least 20 minutes against Germany on Sunday.
Paraguay have not qualified for the World Cup with their focus on the 2015 Copa America.