Hockenheim - Fernando Alonso called on his McLaren team on Saturday to launch an investigation into the car performance issues that have hampered team-mate Stoffel Vandoorne.
The two-time champion Spaniard said a "deep investigation" was needed because there were clear signs of a performance issue manifested by a lack of down-force.
"I think he's doing what he can," said Alonso after he had qualified 11th for Sunday's German Grand Prix while Vandoorne was 20th and last.
"Definitely, the last two races it seems that car has some kind of performance issue, and there are clear signs on the data that there is less down-force on that car.
"We've been changing some parts and we need to go deep into that investigation because with both cars close to the points it is always a little bit easier."
Vandoorne has been out-qualified by Alonso at every event this year and said his car was "undriveable" at the British Grand Prix. He said he had endured the "worst Friday" of his career in Germany.
Vandoorne said it was difficult to accept his predicament.
"Since we hit the ground in Silverstone, we were by far the last car and it turned out the same today. I can't really tell anything more.
"It's frustrating. We changed a lot of parts on the car and it still doesn't work. Definitely, I didn't forget how to drive a car."
Vandoorne's misery is just one more part of a slow crisis that has consumed McLaren this year as they and fellow former-greats Williams have suffered slumps in form.