"I believe it is very good. I am still being assessed but to me it is good and I will be okay," Iwobi told Sky Sports.
"We will have to wait and see but I believe I will be okay and fit (for Atletico)."
Arsenal goalkeeper David Ospina (rib) and midfielder Henrikh Mkhitaryan (knee) are also doubtful for the trip to Madrid after picking up injuries at Old Trafford.
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The north London club need a win at Atletico's Wanda Metropolitano stadium to reach the final after the two teams played out a 1-1 draw at the Emirates last week.
(Reporting by Hardik Vyas in Bengaluru; editing by Amlan Chakraborty)
