Arsenal captain Pierre-Emerick Aubameyang missed Thursday's win over Slavia Prague after he was diagnosed with malaria.
The Gunners have reached the Europa League semi-finals after a 4-0 win in Prague.
And they did without their skipper, who was hospitalised with the illness.
"Hey guys, thanks for all the messages and calls," the Arsenal captain wrote on Instagram. "Unfortunately, I contracted Malaria whilst being on national team duty in Gabon a few weeks ago.
"I've spent a few days in hospital this week but I'm already feeling much better every day, thanks to the great doctors that detected and treated the virus so quickly.
"I wasn't really feeling myself the last couple weeks but will be back stronger than ever soon! Will be watching my boys now, huge game for us! Let's go and get it Arsenal."