An Aleksandar Mitrovic hat-trick secured victory for Al Hilal over Esteghlal on Monday, but the Saudi champions' perfect start in the AFC Champions League Elite was overshadowed by the sight of star forward Neymar picking up another injury in only his second game back since returning after a year out.
Brazil star Neymar came on as a second-half substitute but was then replaced. The 32-year-old forward came on after 58 minutes at Kingdom Arena with Al Hilal already 2-0 up thanks to a first-half double from Serbia striker Mitrovic.
However, Brazil's all-time leading scorer appeared to have a problem with his thigh and, minutes after receiving treatment on the sidelines, was substituted on 86 minutes.
He left the pitch clutching his right hamstring.
Neymar wrote in an Instagam story that the injury will be examined, adding: "Hopefully nothing too much ... It's normal that after one year [out] this happens, the doctors had already warned me, so I have to be careful and play more minutes."
The win puts the Saudi Pro League leaders, record four-time continental champions, top of the standings for West Asia, with four victories from four.
Serbia striker Mitrovic turned in Nasser Al Dawsari’s in-swinging cross on 15 minutes for his second of this season’s competition.
Esteghlal goalkeeper Seyed Hosseini had to be at his best to deny Salem Al Dawsari and Abdullah Al Hamddan but could do nothing in the 33rd minute when Renan Lodi made a surging run on the left before squaring for Mitrovic to tap-in.
The former Fulham striker headed home Joao Cancelo’s cross from the right in the 74th minute to complete his hat-trick.
Next up for Al Hilal is a trip to Qatar’s Al Sadd on November 26 where a win could potentially seal their progression while Esteghlal will face Pakhtakor of Uzbekistan a day earlier.
Firmino on target for Al Ahli
Also on Monday, fellow Saudi side Al Ahli ensured they would keep pace with their Riyadh rivals. Roberto Firmino and Riyad Mahrez both scored twice in a 5-1 win over Al Shorta of Iraq to take the team to a maximum 12 points.
Former Liverpool star Firmino ended an eight-match goalless streak by heading the opener at King Abdullah Sports City Stadium on 14 minutes.
Al Ahli missed a glorious chance to double their lead when Franck Kessie had his penalty saved by Al Shorta goalkeeper Ahmed Basil and the Iraqi side took full advantage to equalise through Sajjad Jassim.
Firmino put the hosts back in front in first half injury-time. Al Ahli then scored three times in 12 second half minutes to blow away Al Shorta.
First, Firmino teed up Saudi Arabia international Feras Al Buraikan, before former Manchester City winger Mahrez struck twice in quick succession just after the hour.
Elsewhere, UAE side Al Wasl were held to a 1-1 draw at home by Al Sadd of Qatar, while Iran's Persepolis and Qatar's Al Gharafa played out the same scoreline also in Dubai.
Soufiane Bouftini was sent off with seven minutes remaining of regulation time to leave Al Wasl to hang on after Al Sadd’s Romain Saiss had cancelled out Alexis Perez’s 29th minute opener for the home side.
The result means Al Sadd remain unbeaten as the league phase reaches the halfway point with Felix Sanchez’s side moving onto eight points from four games while Al Wasl are a further point behind.
