The 20-year-old landed awkwardly in the closing stages of Hearts’ 4-0 defeat at Celtic Park and was carried off with a suspected snapped Achilles tendon.
Hearts’ head coach Ian Cathro, who hopes to complete deals for Greek midfielder Alexandros Tziolis and Portuguese striker Esmael Goncalves today, was already seeking another defender following the departures of Alim Ozturk and Igor Rossi earlier this month.
With Souttar, pictured, now facing a lengthy absence, that area of his squad will become a priority in the hours leading up to midnight tomorrow.
“It’s a bit of a concern just now,” admitted Cathro. “It’s an Achilles issue for John, we don’t know the extent of it just now. As you saw, it didn’t look nice so we are concerned about that. It will be in the next few hours and tomorrow morning before we know exactly what that is.
“We need to get to exactly what [the extent of] it is. It’s an area of the park where we need to add players anyway. We need to add players all across the pitch, including the bench. We are a little bit light. We know we have a lot of work to do and we are doing it.
“We expect to bring in players over the next few days. Whether that [Souttar] directly affects things? I think we’re probably already quite far down the line with a couple of options. We need to just see how he is first. There was a challenge and then he landed from a jump awkwardly, that’s all I know at the minute.”
Tziolis, 31, is a free agent after his contract with PAOK was terminated, while 25-year-old Goncalves’ move to Hearts has been all but confirmed by the president of his Cypriot club Anorthosis.
“These are things that have already been spoken about publicly from the other end, in the case of Goncalves,” added Cathro. “I think the president of the Cypriot club has already made comments so I am sure he doesn’t mind me also commenting. Tzilois is now a free agent, we are working on both of those things. It’s possible but there is still work to be done.”
Despite the ultimately heavy nature of yesterday’s defeat, which leaves Hearts nine points adrift of third place in the Premiership table and now level on points with fifth-placed St Johnstone, Cathro insisted he saw signs of promise in his team’s display.
“We wanted to come here and compete against Celtic and we believed that we could and we gave enough evidence that that was possible throughout,” he said. “We managed to stop their build-up sometimes, but when you play against good players you’re going to spend some time defending low. In the first half we suffered a little more from that but we improved in the second half and our pressure improved also.
“In those situations, when we had the game in our hands, we had to make sure that we hurt them and that the game went to 1-1.
“We could maybe have pushed a bit harder for those opportunities. A couple came but then we pushed a little harder and that was when we lost the second goal and the game started to change.”