Ole Gunnar Solskjaer admitted he did not have the answer to Alexis Sanchez's struggles at Manchester United after the winger failed to make an impact against Paris Saint-Germain.
Sanchez replaced the injured Jesse Lingard just before half-time on Tuesday night but the Chilean was largely ineffective as PSG scored twice within 15 minutes of the restart at Old Trafford.
Solskjaer has inspired an upturn in form for several United players since he was installed as caretaker coach on December 19 but the former Arsenal man is still struggling to find his best form.