Manchester City defender Aymeric Laporte was stretchered off after just over half an hour of his side's clash with Brighton after hurting himself in a heavy challenge.
City hosted the Seagulls on Saturday hopeful of overtaking Premier League leaders Liverpool, who play later away to Burnley.
And their bid to regain the summit enjoyed a perfect start when Kevin De Bruyne fired Pep Guardiola's men in front just two minutes into the game.
But celebrations were muted around the Etihad Stadium following a potentially serious injury for their centre-back.
Laporte flew into a rash tackle on Brighton's Adam Webster, leaving both men on the turf.
Webster was able to regain his footing, however, while the ex-Athletic Club man stayed down in visible pain with an apparent knee complaint.
After receiving treatment City called for the stretcher, and he was removed from the action with 36 minutes showing on the clock.
Fernandinho entered for Laporte, who also received a yellow card from referee Jonathan Moss for the original challenge.
The Etihad subsequently rediscovered its voice thanks to Sergio Aguero, who netted his side's second of the afternoon to extend their lead just before half time.
City will now hope that the former France youth international has escaped serious damage to the joint, as the 2019-20 season steps up in intensity.
While the international break affords some rest, once the club's players return they will have both Premier League and Champions League duties to face, the latter in particular crucial to City's plans this season after missing out in the quarter-finals last season to Tottenham.
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