Nick Heidfeld's recovery from a difficult mid-season phase convinced BMW-Sauber to keep him on board for the 2009 season.

That is the explanation of team boss Mario Theissen, who it was believed was in talks with Fernando Alonso about replacing the 31-year-old German.

"We wanted to decide about our drivers in the summer," Theissen confirmed to the German news agency SID.

The German said the decision about 2009 was therefore postponed to see if Heidfeld could quickly recover from the slump.

"We saw very good progress in the last races," Theissen continued, albeit declining to answer a question about whether BMW simply could not reach an agreement with the former double world champion Alonso.

Theissen said Heidfeld's problems were essentially limited to his performance in the qualifying hour.

"The weakness was not really about his speed in the races, and not at all about his qualities with overtaking, but the fact that he could not get the car right in qualifying.

"We worked with him very intensively on this, particularly on warming up the tyres."

Since the Canadian grand prix in June, Heidfeld has scored the third-highest number of points among the entire F1 field, and ranks behind Kimi Raikkonen for the total number of fastest race laps.

Source: GMM