Despite the unreliable and noncompetitive car, Alonso drove for McLaren in 2016 after he told Dennis he would not go on a sabbatical.
He said he was motivated to improve his form.
At the first race of the season, the Australian Grand Prix, Alonso hit the rear wheel of Esteban Gutiérrez's Haas at 305 km/h (190 mph).
He experienced a 46 g₀ (450 m/s²) lateral deceleration before his car barrel rolled through 540 degrees and rested.
A small pneumothorax on his lung and minor rib fractures caused him to miss the Bahrain Grand Prix on medical grounds and was replaced by McLaren's reserve driver Stoffel Vandoorne, whom he helped.
Alonso out-qualified his teammate Jenson Button fifteen times and scored points nine times.
His highest finish was a pair of fifth places at the Monaco Grand Prix and the United States Grand Prix, and he scored the fastest lap of the Italian Grand Prix.
Alonso finished tenth in the drivers' championship with 54 points, a marked improvement compared to 2016.

He told employees at the McLaren Technology Centre in Woking in December 2016 he would continue to drive for McLaren into 2017.
Mercedes contacted Alonso soon after Nico Rosberg retired and he said he did not want to join them because he wanted to remain at McLaren until his contract expired.
Éric Boullier was concerned Alonso would leave the team at the season's close.
Alonso said he felt McLaren would be competitive and would be unaffected by the emotions of its employees.

Poor reliability marred his 2017 season, especially during the early rounds.
McLaren's engine power performance was lower than in 2016 and it made the McLaren MCL32 unstable at the rear.
Alonso attained a season-high qualifying result of seventh at the Spanish Grand Prix and set the Hungarian Grand Prix's fastest lap en route to sixth.
After taking three consecutive points finishes in the last three races of the season, Alonso finished 15th in the drivers' championship with 17 points.
Jenson Button drove his car at the Monaco Grand Prix, as he raced in the Indianapolis 500 that same weekend.
Alonso was again dissatisfied with engine performance, leading him to publicly criticise the engine and inform Yusuke Hasegawa, the head of Honda's Formula One project, about the matter.
Alonso contemplated leaving Formula One to focus on the Triple Crown of Motorsport.

The McLaren chief executive officer Zak Brown began negotiations to extend Alonso's contract early in 2017.
Alonso considered McLaren's competitiveness in his decision and Brown noted other teams sought him.
He declared he would seek another team had McLaren not convinced him it could win races in the 2018 championship and would decide whether or not to commit after the mid-season interval.
The Ferrari, Mercedes and Red Bull teams were uninterested in Alonso and Brown spoke to him about the situation at the British Grand Prix in July 2017.
He rejected 60 percent of offers put to him from June to August and had not considered the remaining 40 percent.
After McLaren switched engine manufacturers from Honda to Renault from 2018 on, Alonso asked for his future in Formula One to be decided in October.
He signed a multi-year extension with McLaren on 19 October.
Alonso said they had put forward the most convincing argument and believed their chassis had been improved aerodynamically.
Despite the unreliable and noncompetitive car, Alonso drove for McLaren in 2016 after he told Dennis he would not go on a sabbatical. He said he was motivated to improve his form. At the first race of the season, the Australian Grand Prix, Alonso hit the rear wheel of Esteban Gutiérrez's Haas at 305 km/h (190 mph). He experienced a 46 g₀ (450 m/s²) lateral deceleration before his car barrel rolled through 540 degrees and rested. A small pneumothorax on his lung and minor rib fractures caused him to miss the Bahrain Grand Prix on medical grounds and was replaced by McLaren's reserve driver Stoffel Vandoorne, whom he helped. Alonso out-qualified his teammate Jenson Button fifteen times and scored points nine times. His highest finish was a pair of fifth places at the Monaco Grand Prix and the United States Grand Prix, and he scored the fastest lap of the Italian Grand Prix. Alonso finished tenth in the drivers' championship with 54 points, a marked improvement compared to 2016.
He told employees at the McLaren Technology Centre in Woking in December 2016 he would continue to drive for McLaren into 2017. Mercedes contacted Alonso soon after Nico Rosberg retired and he said he did not want to join them because he wanted to remain at McLaren until his contract expired. Éric Boullier was concerned Alonso would leave the team at the season's close. Alonso said he felt McLaren would be competitive and would be unaffected by the emotions of its employees.
Poor reliability marred his 2017 season, especially during the early rounds. McLaren's engine power performance was lower than in 2016 and it made the McLaren MCL32 unstable at the rear. Alonso attained a season-high qualifying result of seventh at the Spanish Grand Prix and set the Hungarian Grand Prix's fastest lap en route to sixth. After taking three consecutive points finishes in the last three races of the season, Alonso finished 15th in the drivers' championship with 17 points. Jenson Button drove his car at the Monaco Grand Prix, as he raced in the Indianapolis 500 that same weekend. Alonso was again dissatisfied with engine performance, leading him to publicly criticise the engine and inform Yusuke Hasegawa, the head of Honda's Formula One project, about the matter. Alonso contemplated leaving Formula One to focus on the Triple Crown of Motorsport.
The McLaren chief executive officer Zak Brown began negotiations to extend Alonso's contract early in 2017. Alonso considered McLaren's competitiveness in his decision and Brown noted other teams sought him. He declared he would seek another team had McLaren not convinced him it could win races in the 2018 championship and would decide whether or not to commit after the mid-season interval. The Ferrari, Mercedes and Red Bull teams were uninterested in Alonso and Brown spoke to him about the situation at the British Grand Prix in July 2017. He rejected 60 percent of offers put to him from June to August and had not considered the remaining 40 percent. After McLaren switched engine manufacturers from Honda to Renault from 2018 on, Alonso asked for his future in Formula One to be decided in October. He signed a multi-year extension with McLaren on 19 October. Alonso said they had put forward the most convincing argument and believed their chassis had been improved aerodynamically.
Motor racing career of Fernando Alonso