He tried to carry on but was eventually substituted after just 20 minutes and left the ground wearing a protective boot.
Martinelli will undergo a scan in the next 48 hours, with Arsenal hoping he has not suffered any serious damage. The 21-year-old has enjoyed a brilliant season and is currently the Gunners’ joint-top scorer along with captain Martin Odegaard.
Arsenal have been hit hard by injuries recently, with centre-back William Saliba (back) and left-back Oleksandr Zinchenko (calf) expected to miss the final two games of the season against Nottingham Forest and Wolves respectively.
The Gunners’ hopes of winning the Premier League title all but ended on Sunday as they were beaten 3-0 by Brighton. The Seagulls scored all three of their goals in the second half through Julio Enciso, Deniz Undav and Pervis Estupinan.
Manchester City are now four points clear of Arsenal at the top of the table after their 3-0 win at Everton and have a game in hand. If Arsenal lose at Nottingham Forest on Saturday then City will be champions.
Pep Guardiola’s men will seal a fifth title in six seasons regardless of Arsenal’s result at Forest if they beat Chelsea at the Etihad on Sunday.
“It looks difficult to be honest, we have to be realistic. I don’t think City are going to make many mistakes now,” said Gunners skipper Odegaard.
“The only thing we can do now is get back and finish the season in a good way. I think everyone deserves that, especially the fans. That’s the only thing we can do and we’ll have to see.”