Fosu-Mensah, 22, was recalled at left-back against Crystal Palace in the absence of injured duo Luke Shaw and Brandon Williams in what was his first stint at left-back since his United debut.
The Netherlands international went three years and 56 days without appearing for United, who triggered the one-year extension in his contract earlier this year, and Solskjaer preferred Fosu-Mensah over another auxiliary left-back option in Diogo Dalot.
Fosu-Mensah sustained anterior cruciate ligament damage on loan at Fulham last year and his return at Selhurst Park marked the Dutchman’s first competitive appearance in 15 months. Solskjaer endured his own knee injury torment as a player and was pleased with Fosu-Mensah’s display.
“On Timothy, 16 months since the last game he’s played, he’s worked hard and delighted for him. I know all about having injuries – knee injuries – and how great it must have felt for him to be out there. He lasted a full game and he played as we wanted him to; he defended really well. We knew it would be [Andros] Townsend and [Wilfried] Zaha to play against; tricky players to play against.”
When asked specifically why Fosu-Mensah was selected over Dalot, Solskjaer explained: “I’ve seen Timothy in training and seen him before with his pace and physicality, and his attributes. We thought he deserved to play this game and he proved that, he showed it.
“He’s going to feel it tomorrow morning but delighted for him.”
Fosu-Mensah made his ninth United start on Thursday night and is in contention to keep his place for the FA Cup semi-final against Chelsea on Sunday if Shaw and Williams are still unfit. Fosu-Mensah lined up in the 2016 semi-final win over Everton at Wembley.