Most of United's business during the winter window looks likely to centre on outgoing deals. Both Memphis Depay and Morgan Schneiderlin, who have not made Mourinho's match day squad since November, have been told they can leave Old Trafford in January, providing the right offers come in.
United had been heavily linked with Benfica defender Victor Lindelof in a deal reportedly worth £38m (€43.8m), but the re-emergence of Phil Jones and Marcos Rojo's impressive run of form at centre-half has seen their interest cool.
While Rojo is suffering from a minor muscular injury and Eric Bailly is currently on international duty at the Africa Cup of Nations, Mourinho sees no real need to add to his squad.
"I think that in this winter market we will only sell and not buy, it is my feeling," Mourinho told Portugal's Sport TV. "Let's build to attack the market next summer as we did this [season]. We hired four players [Paul Pogba, Zlatan Ibrahimovic, Henrikh Mkhitaryan and Bailly] and we knew they could help."
Schneiderlin, meanwhile, now appears on the brink of leaving United after just 18 months at the club. The France international has today (Wednesday 11 January) travelled to Everton's Finch Farm to undergo a medical ahead of a reported £22m move to Goodison Park.
Speaking after United's 2-0 win over Hull City in the first leg of their EFL Cup semi-final, Mourinho effectively confirmed the move. "[I know] no details but before the match I was informed by [Ed] Woodward that the situation is to close," Mourinho said post-match. "Morgan is more than probably going to Everton."