Rosenberg has netted three times in four pre-season games.
And Keen has highlighted the Swedish international's mental toughness as a key factor in his promising form.
"Everyone in the dressing room, and the staff, knows what a super professional and good player Markus was last year - and will be this year," Keen told the Albion website.
"It didn't quite happen for him last year for certain reasons. Shane and Rom hit it off straight away and shared most of the forward duties.
"When Markus went into the team it was difficult for him to make an impact. But we've seen the quality he's got every day in training. His finishing is phenomenal. Everyone in the dressing room sincerely hopes he gets games this year and, if that happens, we're sure he will score goals.
"There would have been times last season when it was tough for him. But I think he's such a good professional, and mentally so strong, that he's just carried on.
"He'll keep trying and giving his best and I think the supporters appreciate that."