Everton boss David Moyes has confirmed that Phil Jagielka will need surgery on a badly gashed ankle.
The England international was replaced just five minutes into the 3-1 win over Reading after being caught by Royals striker Adam Le Fondre.
Moyes said: "I genuinely haven't seen it again but I thought on the pitch it didn't look good.
"Jagielka knew about it and it is a bad one. He will have surgery tonight to stitch up his ankle. It is a bad one because he is a key player for us."
Moyes said he did not know how long Jagielka would be out but the 30-year-old must now be doubtful for next week's FA Cup quarter-final against Wigan.
The incident also reminded Moyes of some of the treatment goalkeeper Tim Howard received in the two previous cup matches against Oldham.
"I'm not happy with the challenges on the goalkeeper in the last two games that have put him out and I am not happy with the challenge today that puts Phil Jagielka out," he said.
"I'm not one who minds challenges. I like a bit of that, if that's what it is. I don't mind robust challenges but not one that puts out arguably one of my best players."
Michael Higdon grabbed his 20th goal of the season as Well's blistering start was enough to secure all three points against Hearts at Tynecastle.
The Jambos' new interim management team of Gary Locke and Darren Murray were taking charge for the first time following manager John McGlynn's departure on Thursday, but their side were left with a mountain to climb after conceding twice in the opening eight minutes.
Higdon swept in the opener before Dylan McGowan was credited with scoring an own goal when he failed to keep out a Nicky Law effort.
John Sutton pulled one back after the break as Hearts put the visitors under pressure, but Stuart McCall's side held on to cement second place in the league and condemn the Tynecastle side to their fifth straight loss.
In Saturday's other SPL game, Ross County and Inverness drew a blank in a scrappy Highland derby.
Chances were few and far between throughout the 90 minutes with neither side able to dictate proceedings at any stage of the match.
