Sebastien Haller was a driving force behind Ajax's Eredivisie win last season, scoring 21 goals and assisting seven times in 31 games.
Haller worked closely with Erik Ten Hag during that time and left Ajax for Borussia Dortmund this summer.
Unfortunately, Haller has had to leave Dortmund's pre-season camp after discovering a tumour on his testicles.
It's not clear if the tumour is cancerous or not just yet but the Manchester United boss sent a classy message of support for his former striker.
When asked about Haller, Ten Hag told MUTV: "It's horrible.
"I've a fantastic relationship with him, a fantastic friend.
"It's my striker for several years — when you have such news, it's devastating. My thoughts are with him and his family."
Source: MUTV
